Since you have to transfer along the way, consider your hub waystation first. ZRH is great, more compact and easier to navigate than the four Euro superhubs, and LX business class is nicer than LH, so I'd say that would be top option if you can swing it.

If LX is off the table owing to price or schedule, and it's back to the drawing board, I would rank the four European superhubs this way: AMS>FRA>LHR>CDG. I love passing through AMS but KL/DL are not always easy to deal with, especially if you have delays, weather issues, etc.

Given your Star Alliance preference I'd say LH via FRA should be your next choice. Avoid CDG transfers unless absolutely necessary, which takes AF off the table. There's no earthly reason to consider Alitalia.

EDIT: RTW1 and I posted almost simultaneously, but I see our advice is pretty congruent.