Well, there are tons of writers that don't get my mnumerous faves, so I'll just concentrate on Iron Man.
1) First off, Gillen. He came into the character and wrote him as if he had only seen the MCU flicks. He had him make statements that contradicted previous established continuity, he gave him the blandest of RDJ-lite personalities, and his run was one of the most forgettable ones ever. To his credit, at least he didn't ruin him, he just wrote a boring Tony, but it's evident he didn't get him.
2) Then we have Jeph Loeb. Millar created a very interesting AU Tony over at Ultimates, and then Loeb came and destroyed everything. See, 1610 Stark was different. He was a Sexual Deviant, a Functioning Alcoholic, a Smart-Ass, and behaved exactly like a man with those traits would. He wasn't a bad guy, but he had none of those "humility factors" that they inject in protagonists to make them "sympathetic". It's a trope that I hate, but anyway. Ultimate Stark was pure adrenaline and testosterone, and I loved that. Come Ultimates 3, and he's a drunken mess that allowed his tech to be compromised by "Ultron", and who spends the whole mini being a moppy, moody little man. Loeb took a very interesting AU and completely ruined it.
3) And last, but not least, we have Bendis. The master of fucking things up. The unmistaken lord of destroying everything he touches. Where do I begin? From the tonal shift of Tony's character to a complete goofball? From putting him on GotG only to make a "haha, he can't satisfy Gamora" sex joke? From wasting 7 months and retconning his origins, while ignoring Arno, to basically make his parents... SHIELD Agents? Fucking SHIELD Agents? But nah, it all pales in front of the stupidity that is his Donut Steel, Ree-Ree. He made one of the most paranoid men in the universe give away his tech to a stranger! A stranger! Who's a kid! And that's not even getting into the absolute awfulness that is Ree-Ree as a character. Bendis destroyed decades of established continuity and character, so that he could add that worthless character to the Iron Man mythos. Oh, and here's a great panel, which screams "I totes watched the MCU movies brahs":
Attachment 55858
(I can't even look at her stupid face)
There are so many Goddamn faults in that one panel that it's driving me nuts. The whole Bendis era needs to be nuked, and Ree-Ree needs to be forgotten, alongside the travesty that is Crossing Tony. Even Teen Tony was better than this. Heroes Reborn Tony blows the Bendis run out of the water, and sends it to Mars. It's that bad.
So, yeah, mostly Bendis. Most people would say Millar or Lobdell but nah, I actually found CW Tony good. It is Bendis!Tony, alone, that I abhor. I really hope the next writer retcons everything. I really,
really do...