That makes sense. So I should use strength spheres and luck spheres then? What else is important?
Well if you don't plan to have more then 9999 HP, you don't need to worry too much about HP Spheres.
DEF and MAG DEF spheres are good to have, being hurt less is a good thing. Luck makes Evasion and Accuracy nearly irrelevant however Luck is by far the hardest stat to grind in the game. (Luck effects critical hit and chance to dodge, 255 Luck, 0 Accuracy, and 0 Evasion is actually better then 0 Luck, 255 Accuracy, and 255 Evasion)
Agility is decent if you want to have lots of turns before the enemy gets to act, which is useful against the Dark Aeons, Nemesis and Penance who are also equally fast too.
MP is probably not necessary because there is more then enough default nodes on the grid to get to 999 MP and there is very little reason to ever need that much MP, when you consider weapon abilities such as One MP Cost.
Once you max out STR, DEF, MAG DEF, and whatever else you like. You can probably just fill the rest of the grid with dud spheres just to max it out. MAG DEF is by far the easiest to grind
(One Eye in the Battle Arena drop them and he takes two hits kill since he only has 150,000HP.
Fenrir drops Accuracy Spheres, Pteryx drops Evasion, and Tanket drops DEF Spheres.
The most annoying are Luck and Mag which take long time get, so if you don't want to cast magic much for damage dealing you can make the choice to kill Jumbo Flan over and over to get enough MAG spheres to satisfy that curiousity of having high magic power. However Jumbo Flan is immune to physical attacks and thus must be killed by spells like Ultima, Flare, or Anima's Pain which all three have an excessively long and annoying animation.
Greater Sphere drops Luck and the Earth Eater has the Fortune Spheres you need to activate said Luck spheres, both are a grind to fight having over million HP each.
Ironclad drops HP Spheres, he has 2 million HP, but his armor can be nullified with Auron's Banishing Blade, and two Attack Reels should slay him (Use Entrust to transfer Overdrive gauge to one character to another)
Best of luck on filling in your Sphere Grid and happy hunting.
It was a seemingly endless battle between Reflect, Curaga and Regen but after 30 minutes I won! I was never this far before... then I got Yojimbo and went back to Besaid and...
