Best option would be Lufthansa ORD to FRA, which would also allow for use of First Class Lounge at FRA. If not available now, book the UA metal and search diligently at the 2 week out mark for LH to become available.... Assuming this is for travel prior to mileage increases if you make changes.
If for some reason you are stuck with UA metal, I would still go through FRA. Much better options in case of some irrops. There is a 2nd TG flight out of FRA at night, as well as an LH flight most of the time, to BKK.
Nothing special at CDG, and I don't find much difference in 777 vs 747 on UA.