Why 8 (First Contact)? Because it took one of the biggest threats the Federation has ever faced and made them truly scary. The battle sequence alone was worth the price of ticket.
My favorite was The Voyage Home. I love whales. There was quite a bit of humor in this movie and I enjoyed the way the crew divided up and went their separate ways creating different storylines.
My favorite? I really don't know. Maybe 1 since that's when I really became a Trek fan. But then again I do like the Voyage home and Seach for Spock. I don't really remember the later ones (TNG movies) but I know I have seen them. Let just say I like them all.
I love The Voyage Home too because of the whales and the humor. First Contact was excellent but I don't feel they really did well by the Next Gen crew with the movies. I'm hoping the new one coming out fills me with all the excitement that I used to have for Trek and it's ideals again