Just want to second everybody's advice -- do buy in a bike shop if you can. I bought a Trek, which I recommend is a good brand. And I bought in a bike shop with good service. A few months after I bought the bike, I blew a spoke on the rear wheel and the bike shop fixed it no charge, on warranty. A couple of months later I blew _another_ spoke on that wheel. I asked the bike shop if it was my fault (I'm pretty heavy), but they said no, the manufacturer makes thousands of wheels a day and sometimes there's a bad one. They were on the phone to Trek then and there, and got permission from the company on the spot to build me a new wheel at no cost to me. I haven't had any problems since.
If you haven't got a good shop near you, you should do what you have to do. But that's why picking a bike shop is almost as important as picking the bike.
As a guy who has had back problems, I'd also recommend a bike with cruiser-style handlebars -- the kind that don't require you to lean forward while riding. Not as cool-looking, but much more comfortable.
|