From the Studio Series 86 Dinobot Slug & Daniel Witwicky review thread:
Great question! Here are my picks (beyond Grimlock and Slag who are already pre-determined).
+ Swoop w/ Prof. Morris. The human who once controlled Swoop; initially against his will but later with his consent. And of course, Morris was Centurion who was an ally of the Dinobots.
+ Sludge w/ Joy Meadows. The Girl Who Was Loved by Sludge.
+ Snarl w/ Optimus Prime (as Hi-Q). Okay, in G1 this version of Optimus Prime was actually riding Slag, but since Daniel Witwicky is already occupying that slot (for some weird reason), might as well assign Optimus Prime to Snarl.