LO used to wear a zip up full sleeper, but we've recently transitioned to two-piece pajamas (either short sleeved or long sleeved) and socks. I liked the zip up sleeper because we didn't have to also dirty a pair of socks and it kept her diaper in place and didn't cause it to leak.
She still wears a diaper to sleep in (she's 3.5), so sometimes the pressure of the pajama pants and a full diaper causes some leakage. But, I want to continue to try using the two-piece pajamas so that eventually she can get up in the middle of the night and use the restroom easier. A zip up sleeper with a snap button at the top is too complicated in the middle of the night.