Just did a re-watch of both the original and T2. I can see why some would prefer the original as it is a much more simple movie (I don't mean that in a bad way), and the original Terminator showing some signs of damage and vulnerability creates more drama than an unstoppable force.
But, with that said, I gotta go T2. Honestly, I think it's probably the best big budget action movie ever made.
Despite it being made back in 1990 I actually like the special effects better in T2 than in action movies now. T2 used a mix of live action sequences and CGI. I kinda feel it was the sweet spot for action movies. As good as CGI is today it still isn't quite the same as the live stuff, and I feel like big action movies today have become too CGI.
The story in T2 definitely takes a grander, more complex arc than in the original, but I feel T2 pulls it off almost perfect. Stuff that has a high probability of being corny if not both shot and acted perfectly, like the scene where John sees the two kids fighting with the guns and says, "we aren't going to make it, are we?" comes across well and actually adds to the end of the world vibe.
Normally, when you have a classic movie like the original Terminator I think you're better off making the sequel more simple and grittier than the original. The fact that T2 is able to turn that on it's head is amazing. They were somehow able to make it more complex, but also better. You see in the future installments how hard this is, where I would argue they would've been better off creating a more simple storyline with a less advanced Terminator that showed some signs of vulnerablity (similar to the original).
Between the perfect special effects, the more complex story actually adding to the movie, the acting, the music and how it was done on such a grand scale I have to say T2 was probably the only perfect action movie I've ever seen.