Ok so I am playing a level 20 imperial vampire multi classing as a thief, warrior, assassin and Mage. I had just managed to kill Krosis. I was walking up the mountain and I hear the oh so familiar and friendly chant of a word wall. Yay! So I ran up to it without thinking. And the treasure chest wasn't helping my recklessness. I end up finding myself in a triple boss fight with a random encounter dragon, elder dragon, and Krosis. My first thought well I'm screwed. I dispatched the dragon easily. Killed the elder dragon with some trouble. Then I drank a few health potions and saved seeing as how I just made what feels like 5000 gold worth in stuff off those two dragons and Krosis was being an annoying sniper. Well after thirty seven tries (yes I kept count) finally I get fed up with it and just fus ro dah that undead maggot bag off the mountain. Collected his crap and left. Are all dragon priests the same level? What level are they and who is easiest to kill?
All of the Skyrim dragon priests are level 50. They have different perks and spells, but they’re probably all about the same difficulty. See the UESP article for details on each dragon priest.
Some of the Dragonborn DLC dragon priests are level 60. Zahkriisos has the same level as the player, between levels 25 and 60. So if you have Dragonborn and are less than level 50, he is probably the easiest priest to beat. Beyond that, it just depends on whether you’re susceptible to any specific type of spells. For example, you might find Rahgot difficult as a vampire, since he can use fire magic. I didn’t see any that looked particularly easy for a vampire.
Krosis may have been one of the easier dragon priests for you, since he uses ice magic, which vampires can resist, and his mask isn’t useful for magic attacks. But his staff of fireballs would especially effective against a vampire.