I desperately need some help in determining what kind of bike would best suit my needs, and which specific brands/models I should be looking at. Here is a rough description of my requirements and preferences. I know very little about bikes, so please go easy!

Essentially, I want a bike that is light, fast, and durable. I will ride primarily on the road/sidewalk, but I do enjoy the occasional dirt/light gravel trail. I will be riding in a variety of environments, but 'urban' would probably describe it best. I always ride in the highest gear and, as a result, find that I constantly encounter the same problems. More specifically, I continually have issues with the following:
- Chain stretching/skipping
- Drive train wear (teeth wear out)
- Chain popping off

I prefer:
- Racing inspired look
- Low profile, straight handlebars
- Durable, racing-like tires
- No disc breaks
- High gear, light as a feather

Given my 'riding style' and preferences, I think a single-speed, hybrid bike would be best. I was tentatively looking at the Trek Soho S, with puncture resistant tires, but I don't know if there is a better alternative. Would this be a suitable bike for me?

If so, what is the difference between the Trek Soho S and the Trek District, aside from the carbon belt? Would it be possible to upgrade the Soho S with a carbon belt at a later date? I love the District, but it's just too expensive at the moment.

Thanks for any/all advice!

If you want light, fast, general purpose bike, you need to think of the required tyre clearance. I reckon that 32mm should be sufficient for tracks and trails although if you ride in snow you may need wider tyres.
A fast bike style with suitable clearance is Cyclo-cross and touring.
Most decent brands have a CX/tourer or dedicated tourer in their range. Racing grade CX bikes are not general purpose, they lack eyelets for rack, fender and waterbottles.

Most multispeed bikes really do work better when you use the gears. Your body *also* will work better when you use the gears, since pushing a large gear takes a great deal of strength, and most people do not have enough muscle around their knee joint for that to work well. Do it long enough, and your knee joint will just fail. A "racing" oriented bike will often have a high gear of 120-130 gear inches. Most singlespeed bicycles will be at 60-70 gear inches. A singlespeed mountain bike might be well under 50 gear inches.

You aren't going to find a bike that is a single speed and is geared as tall as you say you want.

I have a Soho S that I ride to work nearly every day. It's a blast to ride, but I live a couple of miles from downtown, so everywhere close by is pretty urban. I would not take it on anything worse than a well packed, very smooth trail. The tires that come with it are very easy to puncture. I also wouldn't mix racing like tires and gravel, just sounds like it could make for a bad day, imo.

Thank you for the responses. Please be patient with me as I'm still learning what my requirements are.

I'm starting to think that I want a bike exclusively for the road - I'll keep my existing mountain bike for the occasional off-road trail. At the very least, repairing the bike will give me an opportunity to actually learn something useful. I also understand that you're not supposed to ride uphill on the 21st gear (knees shouldn't be grinding), but my chain would ALWAYS pop off when I changed gears... I'm certain there's issues with the drive chain and derailer.

Anyway, I still like the simplicity of a single-speed, so I would appreciate more feedback in this regard. Since I continually encounter issues with the drive chain, I really like the idea of a belt-driven bike (hassle free, virtually no maintenance). As a result, I was looking at the Trek 2nd District as a potential candidate. This way, I can upgrade to the belt drive at a later date (hopefully when the price is more reasonable). My only concern with this bike is the durability. Can this bike handle the occasional bump on a city street, or should I be wary of it? If it is a suitable commuter/road bike, should I change the tires to something more substantial (say, puncture resistant)?

Once again, thank you for any/all feedback!

I'd look at the Jamis Coda. It sounds like it would fit your need. Fixed gears or the Trek Soho can't help much about.

I really can't say why you are having problems shifting and problems with your drivetrain without knowing something about how you ride. You should shift gears before you need to and avoid cross chaining if possible. You should also clean and lube your drivetrain when needed. There is plenty information available on the internet.

No drivetrain is 100% maintenance free. Anyone who tells you that is lying. Singlespeeds are a bit easier and cheaper to maintain, since there's very little fiddling involved. But you're still going to want to take a poke at it about once a month, to make sure the chain is secure and isn't wearing out. A belt drive will not have chain lube, but is otherwise about the same. I don't know about belt drives, but the usual plan on singlespeeds is you replace the chain, chainring and cog all at once. I'd guess you would start thinking about the swap about every 10k miles or so.

It sounds like you *might* be a good bit like my partner in terms of riding style. He's a smallish Clyde (about 220-230lbs), with short stumpy tree trunk legs. Mostly on a bike he gets by due to brute force... which would be fine except he has to keep up with me. I'm a lot smaller, and I am not very strong at all, but I can spin. And spin. And spin.

He did go singlespeed, but he's riding a much lower gear than he's used to, and going a lot faster. He knew going in that singlespeed would force him to learn to ride a bit more like me, and that was a big draw. So far, seems to be working. Before, 10 and 20 mile rides were very hard on him. Now, the problem is never that he's running out of gas in the legs, so it's a big improvement.