I am using M+M/Lufthansa and AA/OneWorld.
The M+M program is good for paid First and Business. AA is good for economy travel (esp. in the US).
OW is good for Asia/US - CX and JAL are fairly good airlines and have good connections for my usual places (China, Vietnam, Hong Kong to LAX), QF is good for Australia. Europe/US is a problem with the AA program: No miles on BA, Finnair and Iberia have limited routes and AA is plain horrible (think United but worse).

Skyteam is also limited between Asia and the US. Delta just stopped flying to SGN (after starting that route a few month ago). VN does not fly to the US (and their business class is like from the 1980s).