you definitely want a variety of types of partners to train with, both in terms of size and bodystyle BUT also getting used to the different games of bjj. it is also great if you get to train with some folks who's grappling base is not bjj. catch wrestlers, judoka, sambo dudes and luta livre types all feel different to roll with. pure wreslters as well but in a way not so much as the wrestling base does not have submissions so as wrestlers train more and more in bjj they become less and less alien to the pure bjj guy.
in my experience anyway