IMO opinion, LH is a better product in terms of lounges, service and food, coupled with the opportunity to use the F terminal and get limo to plane on LH at FRA.

If you're a solo traveller, the LH346 (with its single F window seats) to MCO is a good option.

I haven't taken the new UA F, only the old one, and it was a very long way from being special. LH is much better. Can't comment on the new UA F.

Decision might come down to how many miles you have spare....