It really depends on the situation
If your fighting a boss, Valor FTW. Best place to level up Valor is the Collonade in Disney Castle. You know what I mean.
If your fighting a lot of heartless, Wisdom FTW, Though Wisdom is the best form to use against Grim Reaper. Best place to level up wisdom is... Well, anywhere, really. Where ever there's heartless.
If your fighting strong heartless, Master FTW. Best place to level up master is in Missions where you fight heartless.
If your on the final boss or in the final world, Final FTW. Best place to level up Final is the Final world.
Anti is never FTW. It looks cool, but it can kill you.
I've never used Limit, so I wouldn't know.
If Xehanort without an X spells Another, then chances are the apprentice is the Xehanort we know and love to hate.
But if Terra were Xehanort, then there's a strong chance that Ven is Sora's father. Or at least related to Sora, due to the fact he resembles Roxas and Roxas is part of Sora.
