I like the LH soft product better, and think the hard product about the same, though I have not flown the new Polaris seat.
I always book through UA.com, though, not for status, but because Mileageplus miles are more useful to me than Miles&More. Also, the change policy for nonrefundable tickets is very flexible on UA and other US airlines (basically a credit less the change fee, usable on any other ticket within a year), and not on LH or other EU airlines (generally, must rebook between the same cities prior to the original departure date).
The LH Senator lounge at IAD is one of my favorites there, but it does take more time if you are flying domestic UA from C/D, where even the UA GFL lounge is inferior. I would not go early just for it, but if I am there early, I will go. The TK lounge nearby is nice, too, but has become more crowded than LH.