It's a LOT easier to map in VX, although there is a lot less freedom considering there are only two layers. Many features returned from 2k/3, although the use of fogs was lost. There is an easy, time-saving event creator that instantly creates chests, doors, transfers, and inns. Parallaxes show up in the editor, which opens up many, many possibilities.
XP is harder to map in, but maps can be more detailed. You'll definitely find many, many more scripts and resources for it because it's been out twelve times as long as XP.
I prefer VX, mainly because I cannot map in XP to save my life. I also do not like the solid white transparent color in the Editor, but that's just me. It'd really up to you to decide which you will use.