Hello wahudi, and welcome to FT!

You're certainly on the right track by asking about which program to join, and wanting to make the right, single decision. Most people recommend sticking to one program per alliance to maximize benefits related to elite status.

Since Air Berlin isn't yet part of oneworld, and is currently only partnered with AY and S7 in its FFP, you'll want to find a way to earn those miles now. The Qantas (note the absence of a u in the name) program is well liked by many, as are the BA and AA programs. Some programs have minimum-segment requirements (e.g., having to fly at least 4 segments on the planes of the program sponsor), so you'll want to do some research there. You'll also want to consider what benefits you're looking for in an FFP (i.e., elite status, lounge entry, ability to book award tickets, etc.) when deciding. Something that is most decidedly out, however, is merging of points after accrual - this just doesn't happen.

At AA, 50k miles flown per year will get you mid-tier status, allowing you access to airport lounges when flying outside the North America, Mexico (except MEX), and the Caribbean. This program is possibly the least dependent on fare type, if you plan on flying mostly economy fares. On the other hand, BA and QF's status system rewards full-fare Y and business-class passengers with a quicker road to status.

While I haven't been able to provide you with a suggestion as to which program to pick, if you could provide more specifics as to how many miles you expect to fly and in what class, that might help the experts on the oneworld FFPs here to give you some more insight.

Peace.