Well, I'm limiting myself to three spheres because that seems reasonable and common.
Metamagic: Because if you're going to learn magic, you might as well learn magic, you know what I'm saying?
Creation: I did not pick this, although I wanted to, because I think Creation and Entropy are just too damn good. Call them "fourth" spheres you spend a long time getting to, and certainly not ever mastering. I'd pick Creation over Entropy 'cause that's how I'd roll.
Force: This is telekinesis, right? If it isn't, I'll go with Air, but if it is...TK is the catchall of special powers. You can fly, enhance your attacks with raw force, even TK control your opponents by physically manipulating their bodies. Force owns.
Enchantment: Magic swords, loyal golems, sex appeal...definitely an awesome sphere.
Mind, Body, and Spirit would make a cool trio.
So would Nature, Life, and Death. Mmmm. I'd keep my hand in Death just enough for skellies, because every badass needs an undead army.