I own Real flight G3.5 and I like it a lot. There are a few minor issues but nothing major. I've used FS-1 at the hobby shop. It looks like a great product and might be a little more user friendly than Real Flight. The only real drawback to FS-1 that I saw was fewer airplane options. I also didn't care for the controler; the one in Real Flight is more realistic, just like a Futaba transmitter. It probably boils down to what airplanes you fly. If you have something from Hobbico/Great Planes, go with Real Flight. If you have something from Hangar-9, you might want to go with FS-1. I don't think any simulator can ever replace actual flying but they are good for learning a lot of basic skills without destroying real airplanes. Plus, they can be a lot of fun. Just my opinion of course.

Also, make sure your computer is adequate. Without enough memory or a good video card, you'll be disappointed in any simulator.