Friction shifters are more easily fixed than integrated shifters. Downtube shifters are an easily-repairable option, too, but I don't like to drop my hand down to shift. I did it all the time (I didn't get a bike with integrated shifters until 2004), but for me, I like to keep both hands on the bars.

Sidepulls get out of whack. I like cantilevers, some folks like centerpulls.

The main things to remember is to get a bike that fits properly and to keep it simple. Steel is more comfortable than aluminum, in my opinion. I like the LHT and the classic Trek 520. They have what's needed, and not much that's not needed. I've heard good things about the Jamis Aurora, but I haven't checked it out in person.