FRA - SFO in C / LH or UA?

flying via FRA to SFO in a few weeks and have the option to fly with LH or UA.

The schedule is fine for me with both airlines - so I'd like to make my choice based on the quality of the C Cabin.

I've never been on UA.

How is UA C compared to LH C?

The fare basis will be "Z" - any chance to upgrade on UA with miles?

Thanks