Thinking about it now, if I pick a character who I think has gotten worse than better, I'd say Blaster.

I loved Blaster as a kid. He was a fun and quirky character, who transformed into a boombox (rare for an Autobot), and he sounded like Cat from Red Dwarf. The Marvel comics made him shine; he had a lot of good moments like his rivalry with Straxus, and the time he clashed with Grimlock over leadership of the Autobots. The IDW version, which is most recent, seems to me like the weaker portrayal of the character. He seems so generic, with very few stand-out moments. Also the fact that he sided with Getaway in MTMTE makes him seem more like a tool. I know it's a different continuity, but C'MON; he lead an Autobot Civil War against Grimlock!