TOS: Probably George Takei.
TNG: Marina Sirtis.
DS9: Probably Terry Farrell, although they were all very good.
VOY: Wang.
ENT: Montgomery. As Dane_Whitman said, he seems like a nice guy, but he's just not a great actor.
TNG: Marina Sirtis.
DS9: Probably Terry Farrell, although they were all very good.
VOY: Wang.
ENT: Montgomery. As Dane_Whitman said, he seems like a nice guy, but he's just not a great actor.

). However, being a TNGer, let me consider DS9, the show with the most character development: here is where I can tell who made the most delivery out of the character development given to them.
When he's around Avery Brooks, it's the latter who shines (but that's expected). When he's around Aron Eisenberg, however, it's still the latter who shines! Heck, when he was around Ashley Brianne McDonogh (the crybaby Chief Petty Officer) in "Valiant," she outshone him!