It really depends on how far you extend teams to be included as "one of the best ever". I think Liquid is somewhere in the top 5, but they could be 5th. Without the benefit of them playing against the best teams of each year I think this can only be a subjective evaluation.
If we can assume that the game is on a continual arch of improvement (an easy argument to make), then Liquid pretty much has to counted among the top 5, even if they aren't 1st. To say other wise is to suggest that the completeness of the games in the top teams over last year and this doesn't trump individual performances by teams in the past. And yet, we only have to go back and view past matches to see what plans were executed by teams and how they adjusted to mid-round changes, and how they utilized their nades and such. Go back to 2015 matches and view them to compare. I think it'll be quite clear todays teams are much more complete.