In my opinion it very much depends. I'd rather risk a misconnect at EWR where there are tons of options to get to ORD, rather than at FRA where if I miss the flight I'm delayed by 24hrs.

It also depends on flight times, do I have a tight or long connection at one end vs the other, do I have to get up at the crack of dawn or am I connecting to the last flight of the night.

Also the OP needs to weigh up availability, the ability to waitlist on UA metal and the repricing of partner awards post 31st Jan. Not to mention the tradeoff between LH C and UA C and shorthaul UX vs LH.