Hi. I don't know much about FF and *A in particular but I'm willing to learn. Here's one basic question: suppose that I have a MP account and I fly with another *A airline. Do I have to request the miles to go into MP? Will miles go ONLY to MP and not to the airline's native program?

In general, I'm quite confused about to which degree (if any) partner airlines miles are intercheangable. Do I have to consolidate all my miles in only one program? In that case, can I still fly with a partner? If an airline has a good promotion, like the triple miles from US right now, is it possible to get those additional miles into MP? (I would guess the answer is no).

Thanks in advance

When travelling on a Star Alliance airline, you may have your miles earned credited to any of the Star Alliance airlines' frequent flyer programs, however, you may only earn miles in one program per flight (with the exception of earning PPS status credits on SQ and miles on another airline.) If you are a member of multiple airlines's frequent flyer program, you can not combine nor transfer miles amongst the accounts. For this reason, you should concentrate you miles in one account. Once you earn your miles, they can be redeemed for travel on any Star Alliance airline.

In order to earn extra miles from a promotion, the promotion must be sponsored by the frequent flyer program you are participating in. In the example you gave of triple miles on US, you are correct that a UA member would not earn 3x miles, as the promotion is a US Dividend Miles promotion only for Dividend Miles members. Likewise, all of the current UA Mileage Plus promotions only apply to members of UA's mileage plus program. Sometimes there are promotions for travel on other airlines, for example UA currently has promotion for its own members when travelling on bmi.

sorry I have to delete this

Let's give a simple answer to simple question.
Your miles can go (once only) into any program you want but, as Lurker says, best to keep them all with your MP account. They'll be credited to your chosen program automatically as long as you provide the account number at reservation and/or check-in.

Now, which program gives you the best perks and mileage deals...that's a more complicated question

Thanks for your answers FTs! I have now a more clear idea. I'll consolidate my miles into MM since UA and AA are the only Airlines going to Argentina (where I'm from) from Seattle, and I already have their affinity card.