My character Kwildar, actually took such a convoluted path to get where he is, completely for RP reasons. I actually started the game with nothing more than a really basic costume, a fairly bare-bones character concept, (with some very basic skills chosen) and the Common list. I actually let him, through roleplay, determine what lists he would open, and when. He first decided to be a Cleric, then at around fifth level, for RP reasons, he decided to join the Witch Hunters. Now, at 12th level, he's looking quite seriously into becoming a Priest as well.
From a mechanics standpoint, I would definitely NOT recommend starting play as a Commoner. You would have to open your first list in game through teaching, and would be stuck in what I termed to be 'pre-requisite hell' for about three-six months before you get any of the 'useful' skills (I was playing for four months before Kwildar could cast his first prayer) and Kwildar feels very 'underpowered' to me, compared to most characters who are around the same level as I am.
From an RP standpoint though, letting the character make those decisions, about what to learn, and when, has made this character quite possibly the most rewarding character I have ever played in my roleplaying career. It can be really interesting to see what influences a character's decisions, and how they might deviate from what you would have chosen.
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Lawrence Starling -- IG
"Really, bee! I don't smell flower-y!"
Malcolm Mallardi -- OOG