i respectfully disagree with the poster who suggests you join several. Although you might not make it every year, it sounds to me like you may make silver on one of the three domestic skyteam partners. you certainly wont do that if you hopscotch from one program to the next... But i suspect you already knew that, and that is why you asked the question in the first place....

my advice is join co or nw. those airlines give you unlimited upgrades for domestic first. you might only get them once and a while, but once in a while is better than deltas never. my wife is silver and she probably gets upgraded 35% of the time.

maybe the kicker is that co goes to tel aviv direct from newark. i've taken that flight myself a few times, and they do a good job. although it may not mean much, i always think it's good to be elite, even lowly silver, when flying internationally. the airline tends to listen a bit more, and getting an elite coach seat on a 11 hour flight actually counts for something.

good luck