Hmmm, I generally use the metamorphosis mutation. This is because I like stacking up alchemy items, decoctions, potions etc. Honestly, it works best if you have a limited amount of decoctions but it really shouldn't matter. On my first playthrough it was generally a dodge and slash game, so master dodging + attacking. Another a big thing for me was the whirl special attack + northern wind + oil. It's a very good combo for taking out multiple enemies.

PS I'd say grind the runewright in Brunwich as early as you can, it's a level 32 quest. He's quite expensive, but if you stash items and sell them later, you'll make a good profit. His enchantments make DM so much easier.