If you go UA, you should be aware that they fly to EWR rather than JFK. You will not be given E+ because of your status - you will have to pay for it like anyone else and the price will be about $150+. It only gives you about 4" more legroom - no better food or recline or anything - not even an amenity kit. However, you will get, as a *G, faster check in, fast track security and access to the UA lounge in T2 which is far better than the BA lounges in T5. You will have zero chance of an upgrade to J.