I personally think Aku is a pretty good playby! Whilst in my opinion he doesn't have too many good gifs, he does have solid artwork, like this one which is an absolute menace, or this one which has a more realistic approach, which can be seen as good or bad. Good in the sense that he looks pretty scary, bad because Aku needs flames. In general, Aku's pretty good for a Massassi.
If you really feel like you'd be more inspired to write with the character if you switch the playby, I'd suggest something different from your previous examples. (I've only skimmed through your bio) Since he's a Mutated Massassi, they all look a bit too human IMO. I've always thought that the Witch King of Angmar (Lord of the Rings) suit the Massassi to a certain extent. The helmet just kind of makes sense to me. It's menacing, bound to cause fear to those who are bound to face him - but the protrusions in the helmet neatly symbolises one of the main characteristics of the Massassi without making it overly obvious, which is the growths they have on their head (and back, ofcourse). THIS is badassery.
TL;DR: Aku's dope, but if you want to switch up, the Witch King of Angmar is an unique (and solid) option. No matter what you go for, it'll look great.