My sister's best friend is graduating from college next month and will be starting work at [bigtime NYC-based consulting firm]. I'm helping her plan and price out a leisure trip for this summer and she mentioned "oh, I should get frequent flyer accounts with all the different airlines since I'll be traveling a fair amount on business next year." (apparently she's never done this before )

So I explained to her the concept of alliances and how it's smartest to concentrate on one airline per alliance to earn and burn...

My question is: since she's going to be mostly traveling domestically, the obvious choices seem to be to go with AA (oneworld), UA or CO (*A) and DL (Skyteam). HOWEVER, is there something I'm missing? Due to redemption threshold or benefits or something, is it actually a better idea to primarily credit to other airlines in the various alliances?

Thanks...