Will it affect hitpoints, AC and damage if I choose a fighter/mage or fighter/mage/thief instead of a fighter - berserker?

Does a berserker gain more hitpoints then a cavalier + does a berserker have better AC and damage?

Thanks for the help.

FMT, has a mixture of theif and mage THAC0 and the FM has a mixture of Fighter and Mage. Berserkers have more hitpoints cecause the roll a d12 instead of d10 of hit points, and if you count their berserker rage you gain +2 AC nad a -2 penalty of THAC0 and damage

So if I want a hardcore fighter then I should pick a straight fighter and forget about mage and thief?

Well it depends on what type of char you like to play personaly, ill play with either a FM or a just a plain Fighter.

Barbarians roll d12, Fighters with the berserker kit still roll d10. The HP of the Fighter, Paladin, and Ranger kits is the same for all of them. Which class you pick doesn't affect your spell or physical damage, however, you'll gain levels more slowly, so for a multiclass expect a lower THAC0 and lower spell damage (since you'll be lower level). It evens out a bit more at higher levels, but personally I wouldn't suggest a triple mutli, since throughout the game (I think), and especially at the beginning, you'll have a hard time leveling in any of the classes, which means you'll probably be somewhat mediocre. *shrug* Ac also won't be directly affected by your class (well, not by a fighter or fighter/mage or fighter/mage/thief mutliclass, anyway). remember, though, that as a fighter/mage you can't cast spells while wearing armor, and you can't change armor in combat. *shrug* Just my thoughts.

The more class you have, the les HP you will have, because the hp you get is divided by your number of class when you level.

A fighter mage getting a fighter level would get from 1-5 Hp, He would get 1-2 HP from his mages level.

On the whole, the best Fighter is a Fighter/Mage, because of his ability to cast things like Stoneskin, Mirror Image, Prot. from Magical Weapons, and various spell protections right before a big fight. A Fighter/Mage with those spells up would absolutely WASTE a straight Warrior in a melee brawl, no questions asked.
There are drawbacks, though. If you Dual-class a Fighter->Mage, you won't get the cool Warrior abilities like Greater Whirlwind. And if you Multiclass, it'll take a LOT longer to get your Saving Throws down to the point where you're immune to most spells. Also, you won't get the Berserker's enhanced AC and immunity to Imprisonment, or the Barbarian's greater HP, resistances, & immunity to Backstab, or the Cavalier's Saving Throw bonuses and resistances. It's impossible to decide....but you'll have to anyway.

Thanks anyone. Hmm I'll just go for a berserker once again. Hack and slash is more my type of gaming. I suck as a mage. Standing in the bagground and watching my party being slaughtered isn't me.