Looking at picking up a bike in the next few months.  Going back and forth between mountain and road bikes, and here are the factors going into the decision:

The reasons I want a bike:

• Cross-training/general fitness
• to go on the occasional ride with my wife - she's a newbie cyclist (road)
• I'm not specifically interested in races at this point, but I would like the option to do a few, even if it's just to participate with my wife

Points in favor of a mountain bike:

• most of the roads we have around here are "paved," with capital quotation marks.  My wife takes her bike on routes specifically chosen to avoid the really choppy stuff, but I'd like to avoid that restriction.  I'd also just plain like the freedom to go off-road if the mood takes me.
• I think the mood would take me often.  Even though I'm a road runner as opposed to trail, I fancy myself kind of a rugged individual (even if I do use the term "fancy myself" sometimes), and like the idea of trail riding.
• generally cheaper, from what I can tell (or maybe it's just the models I'm looking at - I know you can spend as much as you want to on anything with the word "bicycle" in its name)
• I am not a fan of the idea of riding at the speeds those road bikes can get up to.  Call me chicken if you want, but I'm just not a fan of going that fast without, you know, a car around me (and yes, when my wife builds the strength to get up to those speeds, I'll be biting my nails the whole time).

Points in favor of a road bike:

• if I do decide to start entering races (i.e. if I get over the last item above), there are a lot more road races in my area than trail.  Some of them, I think, I could still enter on a mountain bike, but I don't know...is that a "thing," to participate in a road race on a mountain bike?
• ...and in spite of the terrible roads, there are still a lot more places here to ride a road bike than a mountain bike.  There are trails around, but I'd have to load up and drive out to them, as opposed to setting out from the house.
• hmm...I guess those are the only two items in favor of a road bike...

so just by making out this list, I may have helped myself decide.  I'm still interested in you guys' thoughts, though, especially on the issue of bringing a mountain bike to a road race.  If I did want to start entering with DW, I'd hate to have to look at dropping another however many hundreds/thousands of dollars for entry into that world.

MTA: And I highly doubt I'll be interested in becoming a triathlete, as the guys in DW's bike shop insist when the subject comes up.  Because swimming.  As in, there are no public pools or non-gross bodies of water around here.

Get both.

The only way to cycle is to always be looking for more gear.

Serious answer is that I use my road bike a whole heck of a lot more than my mountain bike.

Part of that is I have a nice loop from both home and work on fairly quiet roads (apart from dead at 5pm on the work one), so its very convenient to use the roadie.

Last year literally was a washout for our summer, but I expect I'll be using the MTB with a couple of work colleagues who are more into that.

While I don't own one, I'd also suggest a cyclocross based on your needs.

I have a commuter (single speed)

TT bike (triathlon)

Road bike (general riding)

If cost is a factor but you might also want to go off road, skip the mountain bike.  They seem cheaper and ARE in the sense that the cheap ones are cheap POS and will NOT be good for off roading.  If you want to go off road, you're gonna need to spend more money, or expect the bike to die (I know this from experience, having killed two "mountain bikes" trying to off road, and nothing even close to what my off roading friends do).  It's like an SUV, you really gonna take one off roading?  Maybe if it's a Rover.  Not if it's a entry level Honda or Ford.

Also, if you're riding around with your wife, the POS cheap mountain bike is gonna be a brick and sluggish.  Sure, that's good for training since you'll work harder, but it's not fun... do you REALLY wanna work harder?

So...I'm sure there's a difference between a hybrid and a cyclocross bike; what is it?

 

Oh, and if I get a mountain bike, it will have 29" wheels.  I mean, is there some downside to that that would make me want to consider smaller wheels?  Seems like the benefit to speed and terrain handling would make it a no-brainer.

Hybrids are generally VERY relaxed geometry, lower-end components, heavy, and flat-bar'd…so there is only one hand position.  I frankly don't understand why anyone planning to ride mostly on the road or non-technical trails wouldn't want drop bars.  Having at least 3 hand positions really adds to one's comfort.  As my DH is fond of saying, hybrids don't really do anything well.  They appeal to people who look at drop bars and fear that they are only for racing.

CX bikes tend to have more aggressive geometry and a higher bottom-bracket for clearing logs and debris without getting hung-up.  There's a much wider range of quality and componentry available for CX bikes and greater tire clearance to use knobbier tires (I wouldn't consider any bike that can't take Clement PDXs, personally…they seem to be the most popular tire around here, but they are kinda big mofos.  More clearance gives the option to use studded tires in Winter, too).  CX bikes generally have cantilever or disc brakes, which also provide more clearance and less likelihood of gumming up with mud.

If you're considering doing some racing, give CX racing a try (perhaps the best of all reasons to go with a CX bike).  It's crazy fun and not generally super technical.  The people who do well at CX are those with strong aerobic endurance at 5k-like effort and decent bike-handling skills.  Speedy mounts/dismounts often make the difference.  A friend who is half my age and a crazy fast runner (frequently takes her AG and places overall in tris) would still finish behind me in CX races…because my pathetic bike-handling skills are still a bit ahead of hers.  In another season or two I'll be looking at her back.

26 vs. 29" wheels…it's mostly a maneuverability thing.  26" is getting damned hard to find, too…especially with 27.5" (aka 650b) becoming more popular.  I have a 29er…I have some buyer's remorse with the bike.  I'm really at the too-short end in terms of being able to handle it properly (hello, broken wrist 102 miles into the new bike after about a year on a 26").  I got this bike about a year before the 27.5 bikes became more widely available.  If I were to buy now I'd go with a 27.5, no question.  I'm just under 5'4".  A lot of experts don't recommend 29ers for anyone much under maybe 5'7".

Go get a Kona Jake the Snake.   Skip the hybrid.

Forget the one with the aluminum fork if you have any interest at all in taking it off the pavement.  Aluminum in that region of the bike isn't particularly strong.  This is why even entry-level road bikes generally still have carbon forks…and that's for a bike that is designed to keep on the pavement.

I personally recommend Redline for CX.  I love my little Conquest, though it's not particularly light and the components are all low-rent.  I'd kill to upgrade to their carbon Pro with disc brakes…but the smallest size it's available in is one size too big for me.  They only do their tiny frames as lower-end models.  I run into this pretty much with EVERY company.  They don't sell enough of the smallest sizes to bother making carbon molds or equipping them with better wheels, cranks, etc.  Someday a custom frame will likely be in my future (my friend with the Ti CX bike had to go custom for the same reason.  She and I have virtually identical proportions).

My husband really likes his Surly Crosscheck, it works well for our country road which can sometimes be paved and sometimes not.  Plus our driveway is half a mile of gravel and I have gotten a pinch flat on my Jamis roadie before.

I am of the mindset that I need three bikes.  A mountain bike for winter biking, something I can put studs on and fenders, and that I don't mind getting trashed with salt and sand.  A road bike for clear, dry, summer days.  A touring bike with panniers for loading up with books from the library.  So I have three bikes.  I really trashed the mountain bike though, winter riding is hell on components. My shocks are completely frozen up.

I figure, you have one bike so you need spare parts and tools anyway.  So with that investment already made, get multiple bikes so you have whatever you need for the conditions.  

Okay, you guys have about got me convinced on a CX bike, enough that I'll bring it up next time we're in the bike shop.

 

Speaking of which, I will want to use them when the time comes...supporting the local economy and all, but mainly I've been very pleased with how they've handled my wife and her many trials and tribulations getting into cycling.

 

Looking at their website, the brands they carry are Specialized (lots of Specialized), Felt, Bianchi, Kona, Niner, Yeti, Surly, and Scott.  I've seen Kona and Surly mentioned in this thread, any of those other brands have good offerings?

 

MTA: ...and regarding the idea that I'll "need" three/four bikes...of course this could change after getting one and seeing how I like it, but I really am just getting this as something to add into my run training, and if weather/location make a ride unworkable due to the bike I have, I don't think it will bother me.  At least, I don't think it will bother me to the point that I'll want to spend another 10-20 bills on another bike!

Regarding whether you'll "need" 3 or 4 bikes ... I only bike for fun and maybe once a week and I bike/run commute to work maybe once every two weeks.  But I have 3 bikes and they are ALL mountain bikes - one titanium hardtail, one all-mountain full-susser and one fully rigid vintage bike which is my cheapest and simplest yet most highly cherished bike.  Thank God I never have been interested in road riding or I might have 6 bikes!  There's no end to the stuff you could end up "needing"!

Get a road bike.  That way there will be less people on the trails and more open space for me!