which class/kit do you think is the better choice (and why)?

Hmm, neither of them are really "better" it's just up to how you play. I like the Barbarian's Rage a lot more than the Berzerker's ability...

The armor resistriction isn't that bad, you can find some ac 0 chainmail later on in the game, in addition to rings and other items. The weapon resistances are small though, mayber absorbing 20% of damage...

So you will have more hitpoints but you will be getting hit more often...

They're both good though, as their rages give many immunities...

Another problem with the barbarian is the fact that he cannot achive higher than specialized with a weapon...

Definitely a berserker, cuz while raged he is immune to tons of magic, plus most fatal one ie. imprisonment;), besides he can use all magical equipment. I strongly recommend playing a dwarf for his low saving throw vs. magic.