I don't have extensive experience in ICC, and from what I've seen both of these talents seem useful.
Imp cleave for spikes on marrowgar, adds on deathwhisper, adds on boat in gunship(lol), but havent seen much use for it in plague.
Enrage on the other hand is 6% damage during Marrowgar's whirlwind, Deathwhispers aoe bolts + when adds cleave. Nothing on gunship but once again nobody cares about gunship. Nothing on saurfang unless you manage to get blood beasts on you which is a horrible idea anyways.
Festergut seems like it would have some use for it, same with rotface and putricide.
But what about the last few bosses in ICC? What would be more beneficial raid wise overall?
I personally stand with Imp cleave as getting adds down asap = more time on the boss. But correct me if I'm wrong in thinking so.