I would go for scotland - 2 advantages : situated in a map corner, thus more easily defended and lots of good quality troops from the start...

The second would be either the moors (no Pope or excomm : so no limitation on conquest) or the danes...

I don't know how you could find Sicily one of the easiest...

I have to concede that almost all factions are fairly easy (the AI problem) but Italian ones in spite of fielding low-cost/ low-upkeep units have quite difficult starting positions with few rebel settlements to sack in the beginning and warmongering neighbours to contend with...