Whether you pick UA or AA in the long run, I'd suggest you get a US and AA account now and sign up for both credit cards. You should be able to bank a bunch of free miles before the merger. If you are married have your spouse do the same. It'll be a great vacation fund even if you go to UA later on. Not sure how close to EWR you are to keep UA in mind.

If you have a list of places you'll likely travel, I'd review that against non-stops from US, since it might make your life easier...