I too tried the Hitec 5645s and found the centering to be less than
desireable. Roboto's suggestion is valid. Buying 5955s for all of
the control surfaces allows you to grow into a larger model without
having to purchase new servos. If you do not intend to go larger
at any time, then this point is mute. Read closely, alot of the posts
on this site and you'll see "bigger is better" quite often.

Gerald