I tend to prefer wizards, but that's partially because of my old-school nostalgia. Additionally, I feel that the additional level gain required to gain access to spell levels is a highly critical disadvantage at lower levels. Once higher levels are attained, this disadvantage can be greatly offset by the ability to spontaneously apply metamagic feats, greatly increasing the repertoire of the sorcerer. Personally, though, I find their spellcasting abilities to be a bit too narrow in addition to this drawback, thereby rendering them just below playable in my opinion. Granted, their large number of spells per day is quite nice, but they are so limited in versatility by the few spells known that it is basically a necessity to min-max all spell choices to the utmost degree. I find it rather boring to simply cast Fireball every round for ten rounds in a row. The sorcerer doesn't leave much alternative.
When a situation changes such that the narrow scope of spells chosen by a sorcerer become less useful, the usefulness of the sorcerer him or herself varies directly, thereby often rendering the single-classed sorcerer highly inneffectual.
Basically, my decision between sorcerer and wizard is highly contingent upon the level at which the character is initially created. If the character or NPC is starting at 18th-level or above (Possibly 14th or so), it seems to me that the sorcerer is the obvious choice. At lower levels, however, I find the class negatively unbalanced due to its lack of access to each spell level at every odd level. In campaigns I've played, a level gain is generally a large ordeal, not one to be denied to offset fairly minimal advantages. It seems as if the class has been strangled in an attempt to offset its spontaneous casting and high spells per day, to the point that I find it at a somewhat lower power level than the rest of the classes. I feel that some house rules should be applied to the statistics given for this class, such that it might be slightly more effective in combat or something, just to make it a little more unique.
Just my 2 bucks (Inflation)...