Site: Team Inferno because they provide a great service to this community. Many people, including me many times, use the setups posted there as start.
Team: XFR because apart of being such a great bunch of guys, the Online Racing School was an awesome boost for so many people, not only noobs.
League: OLFSL and LFS GT, both are awesome. OLFSL more fun and relaxed, LFS GT more serious, but I enjoy a lot both. DTM is very nice too.
Application: The only one I use regularly is spectator to follow my mates in team events, so my vote goes for it.