The goods and the bads in both games IMHO:
LFS:
+ Multiplayer, best netcode around for a racesim
+ Force Feedback, I can feel when the car will break out (using Black MOMO)
+ Wide range of cars (GT, Openwheel....)
+ Downloadable skins ingame, every user has his own space etc...
+ Very nice Community
+ Great feedback from the Devs
- No real life tracks, sorry, but this is a big minus for me

. The tracks provided are very muck OK, but I really want to drive on real tracks
- LFS is using too much CPU power IMO
Rfactor:
+ Slightly better GFX engine, LFS is using too much CPU power instead of using more GFX card power
+ Wide range of good mods
+ " " good (real life) tracks
- Handling, FFB, I loose the cars too quick, I cannot feel when I will loose the car
- Not enough servers