What matters is run production, so projections should be measured by that. I know that tangotiger (insidethebook.com and tangotiger.net) has used wOBA, which is really just linear weights. Time and time again, he's found that many of the projection systems (PECOTA, ZiPS, Marcel, CHONE, etc...) are all very close to each other. Marcel is as simple as it gets and it gets you 95% of the way. Keep in mind, binomial uncertainty sets the upper limit in projection accuracy. What I mean is, even if you know what the exact odd of a base hit is for a player on every AB, you are still not going to be able to perfectly predict his BA over 600 AB. Over 10,000, you could get pretty close, though.