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The spriggat assassin's is supposedly the best when starting off.
That's right, you get 18000 on beating the game on Brutal. Certainly allows you to quickly level up the rest of the team, as new game+ allows only the Main to keep the stats.
Hmm, this isn't the case in the non-sinisterdesign.net versions. I remember now- Craig updated the sinisterdesign.net version, so that all characters keep their stats.
If you beat the game at a harder difficulty you get more gold. I think the chest by Hellion gives you 18,000 gold after beating the game on brutal.