Is mob XP based on the level or the con of the mob?

[Slave]

The answer is that both are used. The level of the monster is the base, and the con affects that. If the mob is light blue, I've noticed you get AT THE MOST 1/2 the experience you would have if it were blue. This is despite a mere 1 level difference in the mob and his friend that you just killed.

So the ultimate thing to take from this is, kill dark blue cons. They give you full experience AND have a far less chance of melee or spell mitigation than higher con mobs.