I gt the feeling Zoro wouldn't want one and would rather be as strong as possible under just his own power but if he had the map map fruit he'd finally stop getting lost (which would kill the show off) and could target weaknesses. That or something a mirror mirror fruit so he could reflect his damage onto others (was there spmething like this already? oh yeh Kuma's) which undoubtedly most could not handle since he gets ridiculous amounts of damage inflicted upon himself.
For Nami the steam steam fruit. Could f up devil fruit users if she locks them into a room, could help power stuff and unblock her pores so Sanji will want to rescue her til she's 79.