I'm not sure it really matters which one you choose. The CCE manual explains that your movie will have leftover frames unless your frame count is a multiple of four, in other words after all frames have been sequenced there won't be enough to complete another run of the pattern. And so choosing one pattern or the other will result in less frames left out so you have to choose accordingly. Also if you break the same footage up into multiple segments and encode separately, you should alternate them between 2:3 and 3:2. That seems counterintuitive to me but Custom Technology knows more than I do.