Well, it's a bit of both. Frenzied beserkers are the bastard fighters. Their damage is overwhelming. With a high level one, they frenzy and rage for +16str, and then power attack at a x4 for each bit of their base they trade in. At lvl 20, they can trade it all and do an extra 80 damage each hit. However, it gets worse. As said, their frenzy ability can hurt everyone, but the trade off is thus. While they are frenzied, they can't die of damage. It lasts as long as barbarian rage does, which is incredibly easy to push longer and longer.
They'll take a wrath of god to the face (305d6 damage) and still go forward and beat down the mage that did it.
They can solo a hecantcheries (CR 57) for about 20 rounds.
Sure, they die at the end of it, if they've taken too much damage, but by then everything nearby is usually toast too. Party members will usually have a method of not getting hit, so it's all the more nasty.