[greg64]

Caleb, I'd say the answer depends on a lot of factors.
First, how hard are you going to work the engine? If you're just going to cruise around town, the higher CR will probably be fine with the aluminum heads. But, if you're going to tow, and really work the engine up big hills (I live in the mountains) then I'd go with the lower CR.
Second, the cam has a lot of effect. The more radical the cam, the more CR you can get away with (obviously within reason). If the cam is stock/mild, I'd lean towards the lower CR.
Third, how close to the top of the deck are the pistons? The further down in the hole they are, the lesser the squish, which reduces the turbulence, which reduces the mixing, which makes it more likely detonation will occur.