Generally, one of the FF programs with the alliance that you fly with the most. Within that, I would also say generally the one that you will fly with the most, unless one's eaning or redemption basis is better than the others.
Most (if not all) give bonuses based on status, class of travel and of couse, sometime additional bonus like double miles on selected routes. You just have to be lucky with those ones.
For oneworld, I would have said AA, CX and QF would have been the leading ones (particularly AA and QF for crediting discount economy flights on other OW carriers). AA has the distinct AA Gold & AA Platinum Challenge (not really too much of a challenge really :roll: ) Some of the other OW carriers programs I know nothing about, so can't really compare those (and thus this might be a flawed comparison). I have been a member of QF's since 1989 and AA's since 2003.
For Star Alliance, I am a member of Singapore & United. I should have probably joined United's in the beginning (in hindsight), but then again I wasn't expecting to do much travel with *A carriers anyway. I find the United earning very generous (most fare bases are given 100% rather than discounted to 50%) and redemption (particularly in Aust/Oceania) are better - 20K points for a flight anywhere is better than most.
Of course, each to their own. We will probably all have slightly different views as program features will benefit/detract given our own circumstances.