It's super hard for me to choose.
There are things in all three of them I really dig and bring back great memories. But, if you had to force me to choose, I'd say Spider-Man 1. Mostly because Green Goblin is my favorite, and that was the first major Spidey movie and it was so exciting. Plus, it was all new. By the time 3 came out, we had seen Spidey two times before you know? When the first one came out it was just like, super exciting just for that reason alone.
That's the beauty of firsts in a series.
Plus, SM1 had this.
http://www.youtube.com/watch?v=kOrnEFPxhUY
That is one of my favorite movie final fights. I loved the fights in SM2 and SM3, but it was unfortunate they didn't get that brutal. Put headphones on and turn the volume up when Goblin is beating Spidey, it's painful to listen to and I like that.