Depends on the players / comunity you're trying to build.
My server has PvP on. The only time one player died to another was when I accidentally lazor'd DoctorOr.
But that server is pretty damn mature. In case you've got lots of young players, I'd reckon you'd want Yes in PvP. In case you like a little class warfare and potential MFFS and Nuclear battles, then PvP should be fine. Just be ready to restart the map every now and then. You could also use PvP as a test, leave it on, tell everyone that rules are no PvP, whoever breaks that gets a ban...
Other than that, noPvP is imo pretty damn boring, but you if you want lots of girls and peaceful builders / casual players on your server then that is an option as well.