Fighter: "Me strong! Me stab you with sword!" That single sentence just about summed up the Fighter class. If that wasn't enough, Fighters are the game's grunts. They are excellent at fighting, have no magic, move kinda slow, and are quite easy to master. Recommended for newbies.
Wizard: Wizards can cast magic better than any other class (duh!). However, they don't completely suck at fighting, as they can put up quite a struggle with Zap and Augment. Also, in the QFG universe, magic is used for just about everything. Nice class.
Thief: Thieves are back, and now they kinda suck. What the heck happened to these guys? They were SO fun in the past ones (except 3), and now they kinda suck! Still, they get some cool side-quests, like breaking into houses and robbing banks, so it isn't a total loss.
Paladin: The Paladin is basically a Fighter on steroids. They have all sorts of neat skills, like Honor Shield and Heal Touch, and are worth the pain and hardship of getting.
To play as a Paladin: Beat the game once and save the file, or import from QFG2 or 3.
Hybrid classes are a mix between two or more classes. They're created by assigning point values to certain stats in the beginning of the game. I usually stay away from them, though.
Fighter-Wizard: This class is a Fighter with points in his magic stat. At first, this seems to be an advantage, but there's one very important thing to remember: you can't have a sword equipped while using magic. Besides, the armor will screw with the mana fields, making his magic pathetic, and he won't get the cool stuff that Wizards do.
Fighter-Thief: This class is a Fighter with points in either lockpicking, stealth, or pickpocketing. This class truly sucks, since Fighters are naturally clumsy and don't get any cool thief tools.
Fighter-Wizard-Thief: This class is a Fighter with points in magic and one other Thief skill. This sucks for the reasons stated above, and because it only has 50 points left over to assign to other stats.
Wizard-Thief: This class is a Wizard with points in any thief skill. These might work somewhat, but every time I use magic to break into something, I get caught.
Paladin-Wizard: This class is a Paladin with points in magic. This used to be my favorite Hybrid, but it fell out of favor with me in this game. Same weaknesses as a Fighter-Wizard.
Paladin-Thief: This class is a Paladin with points in any thief skill. This simply wasn't meant to be. I think you can piece together why...