Having now painted most of the box sets, of those three, I would say Nicodem. That group's models just have so much character, especially Nicodem, and Mortimer. For me they really offered up the most in painting enjoyment (after a very fiddly construction phase on the zombies).
Pandora's group is OK. I think there biggest down side is that they are so small they really offer less area for a painter to go nuts. To me the only piece that really stands up in a big way is the avatar form. But If you looking to do some cools special effect this would be a pretty good choice.
I'm not crazy about the Victorias. For me one fo the best aspects of painting on the group/crew/army scale is that you crate something that looks like it all belongs together. I like stuff that doesn't look like a bunch of individuales that are stuck together, I like them all to really like that belong together visually. All the models in the Victorias group are so different that I will be difficult to bring that cohesive feel to them.
Over all my favorites have been Nicodem, Lilith, and the Witchhunters. But I rather liked the Beastmasters, and Seamus too.