Re: Endings on FF10-2
To get the best ending in FFX-2 you need to get 100% story completion. You can either do this all in one go (but you have to choose to give the sphere to the Youth League [if you give it to New Yevon you can only get 99% completion]) or you can play through the game multiple times, using the "New Game +" option every time you finish the main game. I did it all in one go, using an excellent 100% walkthrough that I found on GameFaqs (run a search on there under FFX-2, and then it's the one called "Perfect Game Walkthrough", written by nemes1s). I think the 100% ending is worth the extra trouble (though I haven't seen any of the other ones, so maybe it doesn't add that much more).
It took me just over 60 hours to get 100%, and all three girls were at Level 99 by the end (doing Via Infinito, the 100-level dungeon in Bevelle, really levels them up fast, and you get some awesome items in there). Some of the parts of the 100% game are tedious (the most notable being the CommSpheres in Chapter 4, that takes FOREVER), but it's still very doable.
If you have specific questions on the 100% game just ask and I'll do my best to help you.