Have spells in your spell bar! (you didn't mention a class ... kinda hard to respond without knowing a class ... unless you just want spells shared by all 4 caster types)
Not to mention that there are different sets needed for different situations. It's a non-sensical question to begin with. On top of which, with the existence of spellsets, and the fact they are loadable with / commands which can be hotkeyed, there's no need to define a "best set", even if you could.
