As a general rule, I like to sit about 3/4 of the way back.
Ideally, the I should be able to see the entire screen without moving my eyes, yet not have any of the screen off to the side in my peripheral vision. In most theaters, that works out to be about 3/4 of the way back. Then I can just sit still (something I'm very good at
) and allow myself to be immersed in the film's universe.
If I find that I have to sit on either side, then I sit closer to the screen so that the opposite side of the screen is about the same distance as if I sat in the middle of the row.
When "Labyrinth" came out, we got to the theater late and the only seats available were in the front row. My neck hurt for a week after that. Since then the only time I've ever sat near the front was when I took my sister, who had never seen the movie (despite having been to the concert!), to see Pink Floyd's "The Wall". Once again, it was due to a packed theater. Fortunately, since I have seen the film about 100 times, I pretty much closed my eyes and just listened to it instead of hurting my neck again.
When I was a kid I used to love sitting as far back as possible. Then we could throw popcorn or shoot spitballs and never get caught, because everyone else's back was to us!
We were also closest to the exits that way.