My take on this is similar, but somewhat different.
first: consider what class level you will be for a given character level. At 9+ levels a wizard or sorcerer can be a real powerhouse offensivly, but below that they can be V E R Y weak. So ask yourself how much time and how difficult that time will be spent at those early levels. Clerics and Druids are more balanced throughout their leveling. IF you want to go the route of a wizard or sorcerer in a long and difficult campaign during levels below 9, then consider dual (or even tri) classing. In particular consider any of the 10 hit dice classes for a few levels, OR (my favorite) the Monk. If you decide to go this route I'd suggest anywhere from 2-5 levels. Also consider their requirements and the use of equipment (while spell casting).
second: read the spells for each class
http://www.gamebanshee.com/neverwint...zardspells.php
For offensive spells:
in particular look for spells with no saves and no spell resistance. Also look to see how the damage scales with levels. Finally, look to see how the damage occurs (direct like an arrow or and area effect spell like a fireball).
Now look at the other spells:
generally defensive and summoning, but also counter offensive and enhancement spells. Note what spells can be substituted via potions and scrolls. Typically the latter two (counter offensive and enhancement) are easily aquired via scrolls and potions. You will find that it is fairly rare that you will ever need a dispel spell, and a little less rare that you will need a purge invisibility spell (or true sight). Because of this rarity it makes a LOT more sense to simply use scrolls for those infrequent times. The same is true of something like bull's strength, why use a spell to acomplish what a potion will? The only reason is availability, either in price or quantity, or spell duration (and I don't think I've ever had a problem with either).
What I'm trying to suggest here is that there are NOT that many spells you will use, and those spells that are used on an infrequent basis can be acomplished by other means.
If you just want to play with different types of spells then I would suggest either the wizard or the cleric - BOTH have a huge list available. Strangely though, this can be disadvantageous to a beginner. It can often become a matter of "which spell do I use?".
If you will take the time to plan out your spell allocations you will be FAR better served by a sorcerer over a wizard.
Additionally if you decide to go the route of melee combat - seriously consider the Druid. Though the Druid doesn't have more enhancing spells - it does have better, (MUCH better), protection spells via Greater Stoneskin and Premonition.
If your considering an archer based spell caster then seriously consider the Cleric with the Zen Archery feat (a devistating combination -particularly with summons for meatshields).
If you want to go a more purist route and really see what a sorcerer or wizard is capable of then I would suggest the Sorcerer Monk (my fav.). (and with this character you can still play with spells simply by using scrolls.) 2 levels of Monk are all that required.