Rank their power levels, assumed at max strength. Including their minions, artifacts, or whatever else they have at their disposal:
-Vecna (height of power but before divine ascension)
-Acererak
-Larloch
-Szass Tam
(feel free to debate other known liches if they are comparable and not deities or from a setting outside comparison like Dark Sun - magic operates completely differently in that setting so we will aside that.)


Left out Velsharoon because afaik there were never any details or statblocks for mortal pre-deity Velsharoon.
Not including dracoliches, demiliches, or the Dark Sun wizard kings as they are different enough to completely siderail any intelligent conversation on the question of "regular" Lich power rankings.

>>96141606 (OP)
Acerarak is a multidimensional being. Unless the others match that, he kinda wins by default considering you will defeat, at most, just one of an infinite number of him.

>>96141606 (OP)
The L-roach is the biggest 'that guy' munchkin of the lot, that's for sure.

>>96141606 (OP)
Szass Tam is definitely the bottom. Acererak has been canonically killed dead - he just has some clones/simulacra running around these days - so he's probably next. After that I don't know between Larloch and Vecna but something makes me feel it's probably Vecna.

>Asscrack

>>96141606 (OP)
Szass Tam is a hack bitch of a lich with a hard deadline on his so-called immortality that he's already burned halfway through. He didn't even go through the proper channels. He's more like a bitter revenant than a lich.

>>96141606 (OP)
The fact that you need to specify that Vecna has to be weaker than he has canonically achieved obviously means that Vecna is the most powerful. No one else needs a qualifier on them to bring them down to the level of the others.

Acerarak probably would have been the next in line, since he went demilich, but he got himself killed so its moot now.

Acerereak got as strong and as far into the magic tree as any lich can... while still working solo. Vecna was smart enough to realize that having an army of loyal followers is a better line of defense than any dungeon, and instead of rejecting the material world to explore the outer planes as a being of thought he decided to become a god and take a position among the outer planes fulltime.

Acererak was a very smart neet who studied alone, rose to power alone, and died alone. Vecna knew from the start that the greatest resource was actually *people*, not magic.

It's a toss up between Vecna and Larloch, or maybe Iolaum once he's finished whatever the fuck he's doing (don't let him finish whatever the fuck he's doing!).

>>96141606 (OP)
Acererak is stronger than pre-ascension vecna because he himself lifted the bar for evil deities by becoming the god of necromancy and fucking around in ravenloft.
>Szass Tam
He’s been forgotten for so long, we don’t really have anything on him. He has more. political power than the others and presumably has been getting stronger so he could very easily take the spot.
>>96141766
All of these guys fuck around in other planes. Maybe not pre-ascension vecna, I don’t remember the chronology of his life very well.
>>96145405
If you count them as-is, vecna obviously wins. But he’s so old that the shit he had to do at the time of his ascension wasn’t so impressive by later standards. He didn’t fuck around with necromantic stars, for example.

>>96141606 (OP)
in 5e, Szass Tam actually got the strongest statblock of the ones presented (but he's hidden away in AL)