First , without question.
First off, Kyle Reese is a much better character and protagonist than the T-800 or John Connor.
I loved the horror element to the original. More gritty, brooding and darker than the sequel.
I felt in the second film, Cameron probably had less freedom to do what he wanted, given the unexpected success of the original.
The original is a classic. Great story, great characters, great tension and atmosphere.
The sequel is a very good popcorn flick.