I'm stuck on the VX engine, though my sis loves to bug around in Ace already!!
Can't say Ace is better... It's pretty much a combo of the three previous ones.
I like VX for it's easy use. Tough, yeah, more tilesets in Ace! But then again, more scripts for VX all around the globe...
I will stick to VX untill they bring out a new maker, a real NEW maker, not a combine maker
A lack of resources is inevitable with a new maker (though VXAce has been out for a good while now that resources are greater than they were to start with). VX was the same, and XP before that.
For me, VXAce is nicer to work with, but I'm a scripter/programmer so the updated base (both in the code and the options available) is preferred.
Mapping-wise, I prefer parallax backgrounds so the default mapping option is almost irrelevant. Unless you build a lot of the map resources yourself for use with a tile based system, but I think creating a parallax is far easier and time efficient than making individual tiles for specific purposes.
I must say I did enjoy 2k3. I made (read: started and failed to finish) a lot of crappy games for that, but I spent a lot of time with it. Eventing with it was also incredibly fun, and there were a few good games made with that engine.
But from a programmer point of view, VX Ace is a big improvement over VX, and whilst XP has a few nice charms, I could never work with the script editor too well. Everything was all over the place and in badly named places. That, and I didn't like the default sprites in XP. Their tallness is creepy.