I loved the "Hi Christopher, I'm Nero" line. Got a small laugh in the cinema. It's a counterpoint to Pike's seriousness and formality. Pike's concerned and scared, but for Nero it's just Tuesday, kind of thing.
Worst actor in TOS is the Shat. I enjoy his badness but it's still bad.
Worst guest actor I can think of offhand is whoever played Gary Mitchell. YOUFOOLSsoonI'llcrushyoulikeinsects!!!!
TNG is a tie between Frakes and Sirtis. I can enjoy the charms of Frakting but he has several stock mannerisms that he just turns to over and over and over. Watch how he cocks his head back and slightly narrows one eye, that's Ironic Mode: Activated. And he'll grin and jerk his head slightly when he's being That Roguish Riker. Once you spot them, you can more or less call them in advance just before he does them. Sirtis is just not plausible at all. Part of it may have been the made-up accent they lumbered her with, but that can't explain all of it. She never comes across as someone with any kind of qualification or even experience in HR, psychology or any field like that.
Worst guest star on TNG - guy who played Bruce Maddox. He's the only turd in the punchbowl that is Measure of a Man.
DS9's worst regular's probably Nicole de Boer. I don't blame her as it was never going to work, if they were going to kill Dax they should've just killed Dax
and had done with it.
Worst guest is Jennifer Sisko. Just a really weak actress overall.
Too long since I watched ENT and I was never really into Voyager, so that's my lot.