Yes. Go for the spellcaster.

What else are you supposed to do? Lay down and die? Never. Instead, you grit your teeth hard and **** yourself up, your legs literally and figuratively burning. The knight is closer, so you could attack him first. But the spellcaster is clearly the greater threat. He seems more experienced, not to mention he's proving himself capable of casting some incredibly nasty spells.

Trying to channel the agony to propel your movement, you sprint towards the spellcaster who is still arguing with his teammate, but quickly notices you approaching.

"For fuck's sake, I can't trust you to do anything right!" he scolds the knight and raises his hands to cast a spell at you, but this time he doesn't have time to release even a quick spell. Moments after his hands begin to spark with green energy, you've knocked him over and lay your superior weight on top of him, pinning him down and causing him to catch fire along with you. Then you flail your arms wildly, slashing his flesh to ribbons with your claws. He yells in pain, and after a few mere seconds he's dead. Pfft, glass cannon builds...

The flames dissipate, either because you killed the spellcaster or because the spell duration simply ran out. You then lower your head and begin to gorge on your victim's freshly cooked flesh. You notice your low health increase somewhat as you do, telling you that eating dead bodies does indeed restore your health. That's good to know.

You hear the knight approaching from behind you, and your health still isn't even above 25%. But he can't have much health left either, so you stand back up, turn and attack. He does his best to deflect your furious strikes, but he's clearly demoralized by the loss of his two teammates and not used to standing his own ground. One of your hits knocks him to the ground, and you pin him down and bite away his remaining health. His **** is followed by a satisfying *Ding!*, letting you know that your efforts have finally paid off in the form of another level gained. Then you feed on the knight's corpse to the best of your ability, a less satisfying meal than the spellcaster since the armor prevents access to most of his flesh.

Once you can't reach any more meat, you stand back up, your health back at a comfortable value and still increasing thanks to your regeneration ability, and you feel that the debuff has worn off as well.