On-Board:

Hard product (seats, etc) = UA New C wins *hands down*. The NW WorldBusiness is dated and beaten-up. Hopefully they will ....can the product altogether with the DL merger and replace the WorldBusiness seats with the new DL BizElite lay flat suites.

Soft product (food, drinks, service) = NW is more consistent and will be consistently better. UA food is particularly bad (you can search to find many many threads on this)

Lounge:

NW Worldclubs are generally better than UA RCC and unlimited booze is free at Worldclubs (if that matters to you).

Hope this helps. I would definitely fly the new UA C for the seats alone. The rest doesn't really matter (to me at least).

TFD