I used to prefer T2, but gradually came around to the first one. I prefer the atmosphere of the first. It's a bit more raw. I like the Sarah becoming a Terminator, the Terminator becoming a human flip in T2 though. Also that Cameron made a point of the villain being a cop.
“The Terminator films are not really about the human race getting killed of by future machines. They’re about us losing touch with our own humanity and becoming machines, which allows us to kill and brutalize each other,” he says. “Cops think all non-cops as less than they are, stupid, weak, and evil. They dehumanize the people they are sworn to protect and desensitize themselves in order to do that job.”