[QUOTE=crazyb][QUOTE=Blue Order] Aluminum is also very light, as is carbon fiber. The downsides of aluminum are that it gives a harsher ride than steel, and that it develops stress fractures that eventually will break the frame. Buying a used aluminum bike is a huge gamble, because you don't know how hard it's been ridden, and thus, you don't know how close to structural failure the frame is. The same structural failure problem applies to carbon fiber.
I have a Steel Bianchi with 700x23 wheels, and an Aluminum Raleigh Technium with 27x11/4 wheels, and the Raleigh definitely rides smoother. There is a lot more involved in ride quality than just frame material.
I also have a new Giant aluminum with a carbon fork, and the ride quality is excellent. My girlfriends Trek 1000 also rides very nice. My all steel 78 Paramount also rides very nice. Maybe it is design, and not frame material at all.
Originally Posted by Blue Order
Then there's steel. It lasts and lasts and lasts, and the better grades of stel are as light as the aluminum and carbon fiber bikes. A steel frame will not develop stress fractures the way carbon and aluminum frames will, so you can use it year after year after year without worry.
You forgot to mention that steel frames rust.
All these discussions about frame material ignore the fact that the OP wants a nice bike for $200 max. That's not going to get you a used carbon fiber, titanium frame, and it MAY get you a beat up and possibly cracked Cannondale that's 20 years old. Aluminum can be assumed to have a shorter lifespan than steel, unless the steel has significantly degraded (a LOT of rust), or the Aluminum has barely been ridden. I wouldn't bet on either of those possibilities in a hot seller's market like the Bay Area. Sticking with steel (esp. CroMo or better) will just make it easier to find something that's going to be a non-ripoff.