I'm not all that dissimilar, although I do a bit of United domestic flying.

However I went with UA mainly for the mileage redemption. The M&M redemption is a complete joke: huge "surcharge" for any mileage redemption makes it close to worthless, whereas on UA you use your miles plus a tiny fee (you don't get access to LX F redemptions with UA - but overall that's probably a minor issue).

Status earning as described above does vary. Any fare-class on LX earns at least 100% PQM on UA MP. So 4 ZRH-SFO round-trips will almost earn you *G on UA, which is the first worthwhile level (i.e. lounge access, extra luggage). You will however need at least 4 UA metal segments - flying ZRH-LHR-SFO works for that, and is what I sometimes do since flying UA is MUCH nicer than the LX-777 horror, and extra legroom in E+ is still worth it over the A340.)