Well they share a lot of the same lounges, so if you are flying a route that both carriers fly and have the choice between the two, then you get to use the same lounge in either airport, so it doesn't really matter. But I have found that LH
's Senator lounge is nicer than the Red Carpet Club since it has a few more offerings like more food selections, showers and computers. But it really depends on how crowded they are. An empty lounge is far superior to a crowded one regardless of some offerings.
It is hard to go either way again. I have had professional and curteous service on both carriers. LH
might be a little more personable, but I think it depends more on the individual serving. LH
both have their good and bad flight attendants. But either way you will be taken care of and not overly fussed about. Meals are a little slow due to understaffing, but in every other way unless you want someone coddling you like a butler, you will be pleased with the service.
I personally prefer the LH
food. I have flown both carriers on multiple occasions, but have had better experiences with the food on Lufthansa since it seems to be more consitently good. But there isn't a huge difference and it is likely to be up to your culinary preferences. I have found that full dinner services are always superior to lunch even if they both are three course meals.LH
's new seat is far superior since it is lie flat, but also is comfortable in a semi reclined position. But compared to the old LH
seat, I prefer United's seat. To begin with the UA
seat has seven extra inches of legroom and is about an inch wider. Due to the extra size and space, I far prefer te United seat over the old Lufthansa seat.
The verdict is that I would go for United over the old Lufthansa seat since the two carriers are similar in three ways and different in one way. United is better compared to the old Lufthansa and Lufthansa is better with teh new seat.
If you have never designed an airplane part before, let the real designers do the work!