[Draten-Master of Fire and Ice]

Luvian brings up a good point: which class you should select depends upon your personal style of playing. Some people like to use always the same spells, others (and I am only just becoming more like the second type) prefer to tailor the spells they have available to suit each specific phase of the quest. The second method is, admittedly, MUCH harder to play because you have to be somewhat of a psychic (or an experienced RPG'er) to know which spells to choose each time. That said, the Wizard class can be very rewarding to play if you like to put more role-playing time and thought into your game and less hack-and-slash; if not, then you are definite sorcerer material.

A few more points to add:
1. Being a Sorcerer(ess) in NWN is much cooler than in the previous Infinity Engine games because you CAN change your spell inventory when you level up.

2. The Sorcerer(ess) class uses Charisma as it's prime requisite (vital statistic) for determining things like number of spells per level, maximum spell level, etc. so to play a Sorcerer(ess) you need a high CHA. Having a high Intelligence (Wizard prime requisite), however, is cool because you get more Skill Points to distribute when you level up, bonuses on certain saving throws, etc. Bottom line--depends on what you're looking for.