RPG Maker 3 for the PS2 is the easiest RPG Maker in the series; although, because it is easy, you have huge limitations, such as model for characters can only use certain types of weapons.

I am not going over all the details, but if you want to create a fun RPG without learning too many advance techniques, I would suggest RPG Maker 3. If you are into deep custom RPG that do what you design then I would suggest the computer ones (RPG Maker 2000, 2003, or XP) or RPG Maker 2 for the PS2.