I'm NYC based. 2 years ago I would have said Delta - their fares out of NYC tend to be the cheapest so you can rack up miles easy and the upgrades were flowing - anyway thats over so Now I would say go for status on American and churn your way into as many united miles as possible - they really have the best network. That said grab some Avios for shorthauls in the US and Asia. If you can run up 90,000 points in US Air before the merger or whatever is going to happen you can leverage the star-alliance network and use way less points (I'm thinking to Asia - via Europe- specifically) than United.