Just about everybody did a great job during this storyline, so it's hard to pick just one. My personal favorites:
Joshua (pompous, proud, stern and stubborn, funny at times, but despite himself did have a underlining love for his family)
Angelique (she did a lot of rotten things, nearly choked Barnabas to death, turned Joshua into a cat, made Josette and Jeremiah fall in love, made poor little Sarah ill, framed Vicki for her witchcraft, cursed Barnabas, made Josette jump to her death from Widows' Hill....but her evil deeds were so fascinating to watch. Glad Curtis had sense to keep her on the show).
Ben Stokes (though he was resentful at having to be an "endangered servant" (as his descentant the good Professor put it) to the Collins family (particularly Joshua) he proved to be a most loyal servant despite being enslaved by Angelique and a loyal and devoted friend to Barnabas, before and after Angelique cursed him.
Naomi Collins (poor woman suffered so much heartache, it's no wonder she turned to the bottle! But she did have an inner-strength that kept her going....it was just the shock of seeing her son turned into a monster that finally pushed her over the edge
)
And of course Barnabas.....you saw how much he suffered after Angelique turned him into a vampire, how he was filled with so much lonliness and self-loathing....he really made me feel for him.