My vote goes to LX as well because ZRH is just so much nicer than FRA. You'll get some decent sightseeing done in that time to tire out the kids

The hard product is similarly bad, the LH flight is on a A380, so the cabin is a bit quieter than on the 340 LX uses. Depending on delays, immigration with LX is usually faster as it arrives around 30 minutes behind the LH & AF 380's.