I always play wizards, they are my favourite class. They do get to choose a familiar, from something as relatively 'useless' in combat as a bat, to the rather powerful Hellhound, or the ever versatile Pixie. They have a greater variety of spells than Sorcerers, and unlike the Sorcerer, a Wizard's amount of spells is intelligence-based. If you manage to take your wizard to a high level, or even to epic, you get access to pretty damn powerful spells that not much can beat. Some people say that only the Sorcerer can be turned into a killing machine, but you can focus a wizard on offensive spells just as easily. I recently managed to get my female elf wizard up to level 40, and aside from one mishap with a Balor, she's pretty damn much unstoppable and tends to have to save henchmen rather than being saved by them.
Drawbacks: aforementioned variety of spells. There are some spells you'll never use, depending on the mod you play. Wizards are proficient in club, dagger, light crossbow, heavy crossbow and quarterstaff, but not in armor or shields. Arcane spell failure plays a big role for them, so you'll be limited to wizard robes for protection, and the variety to choose from isn't nearly as great as the variety you get to choose armor from. If you want to avoid spell failure entirely, no armor at all.
Wizards tend to die quickly, especially at the lower levels. I can't compare them to Sorcerer because I never played one, but I've always had to take a tank henchman with me if I wanted to survive the first chapter of the OC with minimal reloading.
Melee fighting is also a bit icky with a wizard, especially at the lower levels. For me, that was one of the main challenges of the OC, SOU and HOTU. If you go the 'recommended' way while levelling up, all your points will go toward boosting your intelligence unless you spend them yourselves. Until you get your concentration up, you'll have to deal with spell failure due to concentration failure/break, if fighting in close quarters with your enemies. Additionally, since most of a wizard's feats/skills are geared toward spellcasting, you'll have to decide between sacrificing feats in order to gain a few fighter-related abilities and boosting your wizard-skills.
I'd imagine that Sorcerers share a lot of what I said up there with the Wizard class, but someone else will have to tell you about them.