Lots of standard answers to this, the most prevalent of which is:
what interests you when you look at the rezzers?
Japanese Spirits?
Scalpel-wielding Frankensteins?
Jack the Ripper and his undead prostitutes?
The cold and calculating undertaker that wants to raise an army of undead?
If power is a concern, I think most people would agree that Kirai and McMourning are a step above the others. (Some would argue that Kirai is two steps above)
Seamus is a nice way of learning the game, IMO. His avatar is very fun and when you do decide to change things up and play other masters, you may be in for a pleasant surprise when you do better with them.
But ultimately, I think the standard, "What interests you?" is the way to go.