Which one of them are suppose to be more powerful? To make it fair the Tsaesci in this question is stronger then a average Tsaesci.
1. Ancient Vampire - Powerful vampires that have lived for a very long time.
2. Ash Vampire - Dagoth Ur's best minions, there is only 7 of them.
3. Tsaesci Lord - A powerful vampire snakeman

Are we assuming the Ash Vampire is still alive? Then I'd go with the Ash Vampire. They're immortal and have a taste of divine power from Lorkhan's heart.

But it's hard to say because I have no idea how powerful a Tsaesci Lord would be, but I'm going to assume s/he is the weakest of the three.