The frame geometry on Gary Fischer bikes is a little odd, so you either love them, or hate them (I'm very average build 5'9, 160 lbs so they fit me well).
I've been riding road and mountain bikes for about 10 years (local amatuer competion, mostly triathlon), and I think all of the brands mentioned are good. Aluminum frames are light, good for climbing, but tend to flex, not so good for climbing. Steel frames are very stiff, great for climbing, but heavy not so good for climbing. Unless you are competing at an elite level, you won't notice the performance difference, but you'll probably like the feel of one more than the other.
More importantnly, find a bike that fits your body properly, a good local bike shop should take plenty of time adjusting each bike for you as you test ride it. Get decent components, you'll hate it if your bike skips gears or is hard to shift. Droping the chain frequently also sucks, and if it happens at the wrong time, can be dangerous.
A lot of my cycling buddies spend thousands of dollars on ultra light, exotic alloy, components just to save a couple ounces. My theory is, I'm carrying at least 10 pounds of fat. If I really cared that much about the few seconds I'd save, I'd put in a few extra miles a week, drop the fat, and be even leaner and faster.