I don't recall any difference in comfortableness with the 739 vs 738 at all. The only thing I remember is that just about every one I flew on out of phx was dark. Wasn't it the 739 who had the crappy F seats too? The ones that were "temporary"?

Now a AA flyer I get pretty much all buses out of PHX and they are comfy. The occasional 738's we do get are equipped with awesome large IFE screens and the entire seat itself swivels.