AA is the best in giving miles, e.g. bonus miles, and probably one of the easiest to get to OW Sapphire and Emerald level. However, it is not too good in mileage upgrade.

I used to bank my miles on AA when I travelled within US or between US and Europe often. With my travel most to/within Asia, I switched to MPC several years ago. I found the seat guarantee features for MPC Gold/Diamond very useful in both controlling my budget and booking my flights. Flights to Asia are quite full these days.