If you are on a budget but still hoping to cash in on miles, I would fly AA from JFK-LGB. AA matches JetBlue fares on that route and currently also has a mileage promotion. If you buy 3-4 weeks in advance, you can get a roundtrip for about $250 which is extremelly good for a transcon. AA has a few routes to Europe and has great coverage in South America and of course the US (except north-west). AA does lack in Asia though (only flies to Japan). If Long Beach is a convenient airport for you in the LA area, I would stick to AA. I haven't found DL, CO or UA matching AA or B6 fares. B6 just started their FF program so I would not advise to go with them.