Seat and hub lounges, UA wins. Food, drinks and service, LH and LX win. LX wins over LH. Whether you fly UA or LH/LX you have access to arrival lounges in FRA or ZRH.
Buying business class ticket on united - best to credit to United, you will earn a lot more miles compared to M&M. With a few J TATLs you will quickly get UA status und *G - LH/LX will take a lot longer.