It's a good thing there are so many gears you can use because everybody seems to have different tastes. I find that I can grind up hills in just about any gear so that isn't my main constraint. Spinning down hills is where I'll turn the highest RPMs. If you can't spin, you will want a bigger gear so you won't have to pedal as fast down hill. Then compromise on the flats for how fast you go. 70-72 is my sweet spot right now. I spin like a mad man down some hills yet my speed on flat terrain is very comfortable for long rides.