The one with the female terminator with big diddies. Terrible. There was another one ostensibly from the same timeline with the original actors and Arnie in it relatively recently where Arnie the terminator had settled down and gotten married.
They should have called it a day after T3. It was a pretty high profile release it got in summer 2003, being the first movie in the franchise for 12 years. I actually think it’s a decent flick, obviously not a patch on T2. All the Terminator movies after the third one were merely cash cows.