I don't remember the first one really well, but the best was the second one. This guy who played as the bad liquid terminator was kinda frightening me when I was young. And when I saw him recently in The Unit, I felt exactly the same feeling.. strange.
And, like Izuno, I was expecting the worst for the third one, but it finally turned out to be rather pleasant. I really enjoyed its humor and its end, when you can clearly see a touch of "Back to the Future" (you simply just can't change the future by traveling in the past without consequences).