Knowing that makes me even more inclined to recommend UA. The main disadvantage compared with having *G from a European airline is that you won't get lounge access when flying within N. America, but I'd say that E+ and upgrade opportunities when you do fly UA more than make up for that.

Be sure to read the programm terms and conditions (and in particular to check the earning rates for your most likely carriers and class(-es) of travel) before making a final decision!