unless you specifically want to redeem premium cabin award, I dont see much difference between Mileage Plus and M&M.
I like M&M because once you are gold, it is good for two years, and the 55k mileage bargain to North America sometimes work out well (I'd rather pay a few hundred fuel surcharge than being asked for 160k for a roundtrip biz with mileage plus, maybe that's just me).