I believe the delta reserve costs 400$ (but give lounge access for that).
United explorer will give 2x miles for united flights and is free for the first year +25K miles (you may find more miles on the explorer card). I find more 25K awards available on UA then DL (with UA you can also use your miles on Usair). If you prefer to fly to EWR instead of JFK then UA is a better bet then DL. You may also want to look at the Chase Sapphire Preferred credit card which earns 2x miles on Airlines and Dining. You can use the points to buy airfare directly (on any airline) or transfer them to the UA or BA (for AA flights) frequent flyer program. If I did not have a bunch of credit cards I would go for the Chase Sapphire preferred.