I've used Real Flight and it's very good. The only sucky part is that you gotta buy their $200 system even if you wanna use your own controller. I prefer to use my DX6i.

The Hanger version you can buy without the controller but it's still $169. I havn't played this sim but from the videos and pics, it looks to be a decent sim.

Go to your local hobby stores and see what they got in store for you and maybe play one.

RealFlight has a larger userbase and more 3rd party support with more planes/updates.

After looking at this more, go with the RealFlight if you are indeed gonna dish out the $. The FS One control looks cheap and requires keyboard use more.
The Interlink seems to be the 8channel and probably gives a better feel.