I prefer window seats for the view, and to be near the middle of the plane or forward so I'm not on the plane all that long after it pulls up to the gate. Although slightly behind the wings has its benefits, as watching the flaps can be interesting. Emergency exit rows are nice because of the extra legroom, although I rarely book far enough ahead of time to get one.
I didn't vote for any first/business class because I've never flown it, mostly because it's too expensive, but also because they aren't that common on the routes I usually fly. I'm sure it would be a nice way to fly, but it's well beyond my budget.
The best flights tend to be the ones where I hit it off well with whoever's next to me, though. Despite this, on 1|2 left|aisle|right configurations (the most common config I fly on - very cramped Embraer 135/145's used for regional flights), I've traditionally chosen the 1-width left side a lot - now that I actually analyze it I realize perhaps I should be choosing the 2-width right side more if window seats are available.
As for planes, I like MD-88's and Airbus A319's a lot, amongst the planes I fly somewhat often. Embraer 135/145's are my least favorite, with the Bombardier Q200 probably second-least favorite.