Well, this is a question I would be concerned about as a game maker. XD
This discussion has long went in RPG Maker communities but then it went between developers, each saying what he preferred in each engine and why they preferred using it over the other. But it's time to take another approach to this: as a gamer, does it matter to you?
When looking for RPG games to play, does it matter to you which engine is it built with? I suppose to a gamer, what makes difference is the graphics' style. XP tends to have a more realistic look while VX gives a chibi, cuter style. Do you tend to look at that as a gamer or do you overlook it for the quality of the story and gameplay itself? Do you have a preference or are you neutral towards this?
Curious to hear your ideas. ^^