Rodimus Prime exists in the G1 comics in alternative future timelines, but not in the "proper" timeline (wibbly-wobbly ). In the "proper" timeline, Hot Rod doesn't become Rodimus Prime and instead becomes Targetmaster Hot Rod -- whereas in the cartoon, Rodimus Prime reverts back to becoming Hot Rod again before becoming Targetmaster Hot Rod. At least, he didn't become Rodimus Prime during the original 1980s-90s run of the G1 Marvel comics. The ReGeneration One comics from IDW (which continues the G1 Marvel (Earth-91274) continuity) on the other hand...

But yeah, Grimlock (and the Dinobots in general) are WAY cooler characters (IMHO) in the G1 comics than the cartoons. Actually, most of the G1 Transformers were better in the comics. As Paulbot rightly said, Grimlock (and the other Dinobots too) were smarter in the comics than their cartoon counterparts (although the cartoon Dinobots were more physically powerful). Also, Grimlock is the only Dinobot in the comics who has a grammar impairment. The other Dinobots all speak normally.