My experience is limited to a few:
2-class:
CO BF is EXCELLENT!!!!!!! I would rate it the best Business Class of a U.S. based carrier.
KL Biz Class is great, especially if you sit in the Upper Deck of the Combi 747.
DL is so-so in Biz Elite, forget it in coach!!!
AA's 2 class (Biz and Coach) to South America is lacking. You get better service
in Biz Class in the 777 with 3 classes.
3-class:
UA with the United First Suite. Biz is also good, maybe not recently, though.