Hello. Since I did the same research, let me tell you what I did choose. I got RPG Maker VX Ace.
1] First of all, RGSS3 is better than older core systems. RGSS3 comes with RPG Maker VX Ace.
2] Default characters on XP were two tiles tall. (a tile is 32x32 a pixels graphics square) Character and sprite graphics on VX Ace are 1 tile by default, as all the chartacters that are packed with it. I find this thing prettier, while others might find it ugly. So can you use 2 tile sprites on VX Ace? YES YOU CAN.
3] Map editing is really more limited in RPG Maker VX Ace BUT this is not an argument for taking RPG Maker XP instead of VX Ace. Yes, you can have as many tiles in XP as you want and play with them. On VX Ace you got a limited number. So what do you do?
In case you wanna make somethnig great and nice, having XP or VX Ace doesn't matter really.
That's because you download the FREE editor named TILED and you do parralax mapping using that infinite power tool.
How? Google "Parallax mapping tutorial VX ACE" and find a good one.
CLICK ME!
5] An argument about XP vs VX Ace is that on XP there were a lot of free scripts available.
Today on VX Ace a lot of them are ported and others are made making even action RPG systems available.
So consider VX Ace a better alternative.
6] Music support. VX Ace wins here.
7] By default RPG Maker series is programmed VERY easy by using event commands.
VX ACE has A LOT more and better from XP.
And as I mentioned before, it also comes with enhanced core scripts
8] Interface. Well it is similar but VX Ace feels better really. You just have to get used to it, and learn fast what is going on and what you can do... hmmm... here, take something I made for that purpose. It is a free tutorial game.
9] Starting assets. Both lack some essentials to make a modern game but you are an artist... so...
CLICK ME TOO.
Note that these are my personal conclusions due to my personal research.
I might be wrong on some parts, I don't wanna start a debate or an argument here.
I don't present them as universal truths, but as a personal opinion to help @The Windlord.
Cheers and happy game making.
We are expecting you.
EDIT:
PS: Due to a Humble Bundle that took place, I got both VX Ace and XP.
Edit 2: Fixed some parts that were not making any sense. Personal reminder: Never reply when you are sleepy.