So far played with random HP on level up but I don't like the concept anymore. Too many times I am getting low rolls. Unjustified. Clearly classes have different HD and not taking full advantage of this property is as if amputating the classes. Unacceptable. And emotionally not cool because leveling up is also a rewarding experience and when the dice is low it takes the pleasure of the reward away. Frustrating. Not fun. In some cases for example Dorn gets 40 HP at level 6. Ridiculous.
Fortunately there is an option to always roll max HP on level up and I strongly recommend turning it on.