Whichever one has R inventory available when you go to book.

Assuming that's the same I prefer TK over LH/LX/SN for the intra-Europe hop though mileage earning may be lower on TK than the others for that segment. And I'd probably put MUC/FRA above LHR above BRU/ZRH/GVA/VIE (in that order) in terms of where connecting is easier/more pleasant.