Movie Trailers - Dimensions Vs. Length Vs. Quality?

Im currently putting together six new movie paysites and im in a bit of a quandry about whether to use large resolution trailers, longer trailers or higher quality trailers for the samples on these sites tours.

Do you think one specific feature of a movie trailer makes a surfer more likely to join than another or, do you think it is a combination of all three key features when it comes to sample clips on tour pages that envokes a surfer to click through to the join page and ultimately sign up to a movie paysite?

Are trailers even needed? I know several successfull movie sites that dont feature any trailers on their tours at all.

Regards,

Lee