I will say right now off the bat, I way prefer Shamans to the other two, and after our own playtesting in our local group, the others agree with me (or I with them; either way). For us, Shamans have the advantages of Oracles and Witches without their disadvantages (really debilitating weaknesses for the one; a walking, "talking," fragile spell book for the other). My issue is, I'm not that personally good at game mechanics and construction, so if there's anyone out there who feels like we do, give me a holler; I haven't seen too much in the forums on this specifically. :)
LB