ALL OF THEM. >:D
Reach is the best game Bungie has produced. EVER. =}
IMO halo 3 is better than reach the ranking system also was better in halo 3 even though people boosted in team doubles it still measured how good you are with number skill and not how much credits you get for firefight. I still enjoy Halo Reach but Halo 2 and 3 were better. They were all really good games though.
I think halo 1 is still the best halo game