Wyll is motivated by his own, very selfish, reasons: revenge and finding his patron. He certainly has some mean traits as suggested by that officer of the Flaming Fist at Waukeens Rest, if Wyll is in the party there. So I'm pretty sure, he is a neutral character.
I agree that Wyll is neutral, but I'd not say getting revenge for being mutilated is a selfish act in itself (unlike trying to find his patron). There is no possibility to get justice from goblins, since this particular tribe seems to be on the far end of chaotic evil.
