I think Grievous' situation was both the best and the coolest.
I love Darth Vader all day long, but his suit was a literal torture device and designed with weaknesses for Palpatine to exploit. It's the man that makes Vader cool, whereas it's the cybernetics that make Grievous so awesome, in my opinion.
Also, Maul's creepy junk spider body was was cooler than his humanoid replacement. Definitely not "better," though!