[ericgrau]

I like to break spells into ranked categories:
1. Crowd Control. Barriers, area of effect debuffs, etc. Make large groups into more manageable small ones.
2. Status Effect Buffs. A control similar to crowd control, but targets friendlies. Think of it as the difference between blindness and invisibility.
3. Direct Damage. Almost as strong as the first two, and it's easier to switch energy types than to overcome immunities/counters to the first two. Especially good for area, since the total damage adds up. A more reliable backup.
4. Save or dies. Anything strong enough to be worth hitting alone (rather than using an area spell) probably has a good save, making DD usually faster. But not always. Not to be confused with area debuffs (see #1).
5. Stat buffs (+X). Usually too weak to be worth a round or spell slot. Use your leftover lower level slots for these, outside of combat.
6. Utility spells. Used so rarely you're usually better off with a scroll. You only need a couple per spell since you barely use them, making the scrolls plenty affordable. Don't bog down your prepared spell list with them. Not to be confused with #2.

X. Misc (not ranked). Clever illusions and other misc. spells can be situationally useful. Give them some thought at least.

For your first caster I'd stick to full casting for maximum effectiveness and minimum complication. Go wizard or sorcerer then prestige into lore master and/or archmage if you want. Be especially careful about spell selection if going sorcerer since you can't swap them later. So sorcs may be less work but they're harder to make. Other than that the strategy is the same between the two.