That's a really open question, and it comes down to what you want to play.
If you want to do more of a combat-oriented character, I recommend using a two-handed weapon. This is the most straightforward combat style in the NWN series and it's pretty hard to screw it up. Start with a decent strength score (I'd recommend 16) and increase it as you level up and get access to magical items. You don't have to be a big dumb barbarian, either. I find fighter/rogue is a great multi-class combo that gets the best of both words; the front-line prowess of the fighter with the skill of a rogue. Just don't expect to be stealthy in full plate (use scrolls of invisibility instead - rogues can use scrolls if you take the "use magic device" skill ;-)
If you want to do spellcasting, Wizard and Sorcerer are awesome. It's a bit tricky to figure out which spells work and which spells don't, but aside from that they're pretty easy to play. Pump your intelligence (wizards) or charisma (sorcerers) as high as it will go, and start throwing out devastating magic. Remember that damage-dealing spells are only one weapon in your arsenal; a good spellcaster can disable enemies, buff allies, and summon reinforcements. The haste spell in particular is awesome, turning your entire party into fast-moving jet fighters and I highly recommend it.
Finally, if you want to play a balanced fighter/caster, my recommendation is Druid. It has great spellcasting, including healing spells, it can shapeshift into powerful forms in combat, and in general is just well-balanced. The only catch is that there is a druid NPC available very early in the campaign, so there might be some party duplication there. It's still a great class and if it's what you want to play for your character then go with it.
