I'm with Jackie on Barnabas. He's had over a century of suffering at the hands of Angelique and her meddlesome ways. Julia certainly did suffer with her love for Barnabas, and of course, because she never was recognized by the Dave Woodard Ghost Fund (DWGF) with the coveted "You Cured a Vampire Who Forced You To Kill Me Award". Damn, her name really would've looked AWESOME etched in gold.
And please, don't forget all the suffering that Maggie's 1970PT incarnation had to go through at the hands of Alexis/Angelique/Alexis.
Also, if we're talking in terms of which actor played the characters who suffered the most, I'd have to go with KLS-- 2 Maggies, Kitty, Rachel, Josette, am I forgetting anyone?