I'm not sure why UA isn't a contender, especially if you need the UA metal towards your GS status or if you're heading towards 3MM.
That being said, if it's irrelevant, I'd give the nod to LH here. Even though the DXB-FRA is a 7 hour redeye in a coach seat, the FCT and the nonstop in LH F to IAH are arguably a better choice than LX, even with the DXB-ZRH leg in F. While the F lounge in ZRH is great, the ground experience can't compete w/LH.