There are quite minor distinctions between servants in what they can do; the primary difference is in their quests. The bonus in creature armour rating from the choice of necromancers, which ChrisHLD mentioned in the spoiler, is negligible when using better quality parts.
Sentinel Island Servant picks....Willy is a scam artist, which you could have confirmed if you mindread him. You'll meet him again in the FoV section of the game, but there he will be after your help, rather than your gold.
