This whole thread looks like a list of lawyers' offices.
Okay, I'll take a crack at it for the series I've seen and liked.
TOS: Kelley and Takei (for the people who mock him for his feud with Shatner, just read his autobiography; there's a lot more to him than that).
TNG: Stewart (I loathe Jean-Luc Picard, but have enjoyed Stewart's other performances in other series and movies, ie. Sejanus in I, Claudius and Henry Grey in Lady Jane, with honorable mention to his cameo in Robin Hood: Men in Tights. A second actor would be Colm Meaney. I've seen him in other things that probably didn't make it to mainstream entertainment platforms in the U.S. and he was very good.
DS9: Robinson (love Garak - I have a friend who named her cat after him! True story: Another friend and I went to visit this first friend, and neither of them had met the other. I'd mentioned Garak, and when we pulled up in front of the house, my friend noticed a tall guy out front and asked, "Is that Garak?" I looked around, then realized the confusion. I said, "No, that's her brother. Garak is her cat." I'd forgotten to mention that detail. I also like James Darren (Vic Fontaine).
Voyager: Ryan (is there anything she can't do well? And it can't have been easy to put up with the hostile attitude she got from Mulgrew all that time) and Picardo. These two portrayed their characters well to the point that they've inspired me to read and write Voyager fanfic (the TOS cast did likewise, many years previously). And that's something that none of the TNG or DS9 actors managed.
The rest of the series... either I can't stand them and quit, or found them so boring that it doesn't bother me that I never saw all of them. I haven't seen any of the last three and don't even care.
I could possibly become interested if they ever make a new one based on the ending of the tie-in novel Federation. It's a great jumping off place.