Instead of worrying over which esper gives which bonus, I tend to look for whcih spells I want to use first. For example learning curative spells ealry in the game is essential. Plus learning Vanish and Doom makes future boss fights so much more.... easier to accomplish.

It should be noted that the same strategy that works for us might not work for you. Get a good feel for them, develope your winning strategy. But in all, just have fun.