Quote Originally Posted by Mirage View Post
When you fight enemies that gain you experience points, always be sure to equip espers that give you stat bonuses at levelup. The Stamina stat is useless, and you should save HP/MP bonuses to high levels (85-99), because those bonuses benefit you more at high levels than at low levels, while the other stat bonuses are equally beneficial at all levels.

Doing this means you will often have to equip espers that don't teach you new magic. You should catch up on spells in areas where you don't gain experience, such as at the Veldt (the area of the world map where you meet Gau).
Anyone who levels past 60 is going to be way overleveled, and nothing will be a challenge. It's even pretty easy at 40-50. The items that are available at the end will give you the ability to kill anything without much effort if you have a decent level.

I wouldn't pay much attention to the stat bonuses. Focus on learning new magic, and then equip like vigor, magic, or HP/MP bonuses depending on the character.