That's a toughy, your familiar with the RPG maker 2003, but XP could probably present things that 2003 cant, maybe double techs/ tripple techs for instance.
(An annoying problem with XP is the battle system, but there are scripts to 'fix' that.)
There's always Rpg maker VX, but I know nooothing about that one.
But its the code that drives me nuts XD.