T2 for me. While I love T1, T2 is an improvement over it in every way. There comes a time when you can have too much special effects, and that's why I generally prefer original movies over their sequels, but T2 didn't overdo it at all. In fact, most of the special effects were necessary, especially in the T-1000's case.
Arnold punching his face and him morphing to grab his fist was fucking awesome. Or Arnold slamming him up against the wall face first, and then him morphing himself to have his back against the wall made my jaw drop. Nothing like being able to sink into the floor, slide through bars, and be able to take a direct shotgun blow to the head to make you a badass. That's not counting the fact the thing was able to copy people and form knives and other stabbing weapons from it's body.
In T2, throughout the whole movie you were left wondering how the fuck they could ever take this thing out. I mean, if they never came across that plant, how could they take it out? That's a true mark of a badass villan, imo.
I agree with Force too. That part where the machine is limping makes me laugh as well.