What exactly is the question? Better character overall or whose voice is better voiced by Ms. Fumiko?
Either way, I never got into Hellsing and I didn't think Seras Victoria had a lot of lines. Rukia is a major character in a shonen genre and recently she play a vital role in the filler arc with a lot of lines, so my vote easily go to her.
I watched both Hellsing and am continuing to watch Bleach but I think that because Rukia has more lines and is in the anime more it makes her more likable. I guess you would call it. Her voice is done really well. So, my vote goes to Rukia.