Getting access to 2 flights as a Premier 1K, one with a layover in Frankfurt and one with a layover in Zurich. Both have components of United travel, and are around a 6 hour layover. Never been to either city.

which is the better option?
1) in terms of lounge access
2) in terms of venturing out into the city
3) in terms of economy travel on Lufthansa or Swiss

thank you!