For me, easiest is no contest -- FFVIII. You can immediately augment your stats and, within two hours, get Degenerator! It doesn't help that limit breaks are the most abusable thing this side of a broken ATM.

Hardest that I've played is Vagrant Story. It's definitely refined and nuanced, but as hard as I try, I stumble repeatedly in fighting, keeping RISK down, building and correctly using weapons, etc. Great dialogue in the vein of FFT, but it can crush people going it alone pretty easily. Federal law should state it can't be sold without a manual. =p