Don't know about simplicity, but for durability and hills I'd go with a mountain bike. I bought Cannondale's cheapest mountain bike in 1997 and it's still going strong. Granted, the combination of dropping 300 pounds on it (me) and going up hills so steep I had to hang out over the handle bars to keep the front tire on the ground did tear up a chain ring or two.

Bought my first road bike two weeks ago and love it, but I actually have to be a little careful with it. No more going airborne.