The spellcaster

The fighter's main weapon seems to be his large sword, and you have resistance to damage from swords. In addition your spear has better range, giving you some extra advantage. Therefor taking out the mage seems like the better choice.

Wasting no time you run towards your chosen target, spear aimed at the middle of his back. Both guys ignore you and within moments the tip of your rusty spear bursts out of the robed guy's chest. “How...?” He manages to get out, sounding quite surprised, before his body bursts into hundreds of tiny lights and he vanishes, leaving behind some coins.

“What the hell...?” The warrior is quite surprised by the sudden demise of his companion, but even so he has enough presence of mind to pull out his large sword and slash at you, landing a direct blow on your unarmored bones.

1 damage received.

“ONE damage? What the fuck?!”

You do not give him a chance to finish that thought, or to try a different weapon. Using your full strength – as little as it might be – you stab him in the approximate middle of his torso. His armor blunts the blow somewhat, but it's clearly not enough, because a moment later he too disintegrates, leaving behind a few gold coins.

“Thanks, Mister Skeleton!” You hear the girl's voice and turn towards her – right on time to see her disappear in the thin air. So much about blocking teleportation. You think, then you are distracted by a loud “DING!” sound as a message appears in front of you.

LEVEL UP! Max level reached!