I think MUC is a good choice. *A F pax have access to the SEN lounges. Connections at MUC are incredibly easy, so shorter layovers still give plenty of lounge time as compared to airports like FRA or LHR. The lounges are reasonably nice, including one that's reminiscent of a Bavarian biergarten, but if memory serves, that one is on the Schengen side (at least I used it most recently while nursing a post-Oktoberfest hangover en route MUC-FRA).

FRA has better TG F seats on its two flights, plus the new 744 config on TG920 next month, but the Tower Lounge near UA gates can get super-crowded in the morning. With the exceptions of the FCT/FCL and the 'City Lights' SEN lounge, I find FRA to be an unpleasant airport.

Connections at ZRH are fairly easy too, but I am not terribly impressed by the lounges there, even the FCL (as compared to FRA/MUC). Definitely less crowded, however.