I've stayed at both - for one day - just pick the one with the theming you like best. Now - if there is more than a $15 difference - I'd say go with the cheaper one. $15 is 4-5 bottles of water at theme park prices. Or a full lunch QS entree with drink for one person. Now - maybe that's just a drop in the bucket for you - and if so, just stick with the which one sounds most fun idea instead. If you are looking at a $40 difference - DEFINITELY just pick the cheaper one. They simply aren't a $40 difference, IMO.
The PP who mentioned the advantage of Pop of being able to go see AoA - that's a good point. You do get to easily explore that resort, too. But if you have never stayed at the All Stars - you can walk around to see all three of those, too.