The order is:
High Allagan > Novus > Gerolt's > Weathered Gerolt's / Tidal / Animus > Leviathan
Let's consider the fact that Leviathan's weapon is a dead end. There's no progression past the mirror, unlike the Animus weapon; considering the mirror has such a low chance of drop and once you acquire all relevant Leviathan weapons the fight itself becomes useless in terms of gain. I believe it's acceptable to declare the Tidal path as obsolete right now.
To put it in another context, if someone willing to grind their asses for a weapon asked me "What should I do, Atma or Mirror farm?" I'd answer the following:
"Start on your Atma weapon and do Leviathan until you get the i95 drop, then forget Leviathan exists."
I just think that if someone is willing to spend copious amounts of time grinding for something they might as well invest it on something that isn't a dead end.