Halo 4 brought the franchise back (I don't care if you think it's bad, it got rave reviews and sold like hot cakes)
Halo Reach didn't do much for the series.
Did 4 really bring the franchise back? Granted, it sold very well, but a scary percentage of people have put the game down after just two months. My friends picked up the game for its CoD aspects, and now they only play when I invite them. now, it seems 343 is patching up a lot of issues, but the update may come too late, as it did with reach. And rave reviews? When's the last time you saw a triple-a game earn anything below a 9? If Halo 4 was really the best game ever people would still be playing it.
OT: I like Reach the best, but I didn't play 2 or 3 online.