2 is cooler than 1 because that's when the doc explains that you cannot back into the past of the same timeline as it would be different from the past of your original timeline - that's why they have to go back to the point where Biff gets hold of the almanac...wait! how many times have I seen these movies :Q
1 set the tone, but 2 was really the meat of the concept...so 2 wins :thumbsup: