Original Series: George Takei - very friendly and nice; Nichelle Nichols; James Doohan; Robin Curtis. All seemed to enjoy interacting with the fans.
TNG: Jonathan Frakes -I didn't meet him personally, but he was at our convention. Even though the crowd was very small, he went all over the room and interacted with various people and made it seem like we were a huge crowd honoring him. Classy guy.
DS9: Casey Biggs, Armin Shimerman, Chase Masterson, Nana Visitor.
Ent: Connor Trinneer, Anthony Montgomery, Dominic Keating. Very fan friendly and fun.
I've seen all but Majel Barrett from the original series; all but Dorn, Sirtis, Spiner and Wheaton from TNG; all but Auberjonois, Siddig and Meaney from DS9, only five of ten from VOY and all but Bakula and Park from ENT.