I haven't played a lot but I would figure the intangibles of fire giant/duergar would trump that of felar at hero.

The only thing I see going for felar is the fact that they can dual wield with a spear which gives them an advantage when it comes to vault and to a degree with tanking. And if they get a big weapon they can get decent mileage out of lashes.

If I compare that vs... the inherent bash protection of being giant sized... I personally would go with the giant over enhanced vault chance or arial for inherent trip protection and better lashes once charged up. Heck felars give up the ability to have 2 proging weapons which is somewhat significant once charged up.