Metallica's first 3 albums are great, then they fell the fuck off after Justice.
Slayer were good until the 90's came around and they decided they wanted to be Pantera but minus the hooks.
Megadeth are incredibly inconsistent, they've alternated between pretty fucking good (Peace Sells, Rust In Peace, Endgame) and fucking abysmal (Cryptic Writings, United Abominations, Super Collider) throughout their entire career.
Anthrax were never good.
Slayer
MegaDave and the Wanky Boyz
Dadtallica
Who?
Slayer is the only one I actually enjoy and even they stretched out one album worth of creativity over an entire career. Teutonic thrash > American thrash.
I would rather Cannibal Corpse
agreed, though I really thing Anthrax should be replaced with Overkill to keep with the consistency of having US thrash bands
Why even listen to American Thrash when Teutonic exists?
Slayer > Anthrax > Metallica > Megadeth
metallica > megadeth > anthrax > slayer
perfect.
Slayer
This is the only correct ranking.
Megadeth - unimpressive guitar wankery, not a single decent album in their discography, some of the worst vocals I've ever heard from a commercially successful band, utterly unremarkable sonically.
Metallica - made some fun, albeit terribly aged albums early in their career that are somewhat enjoyable if you're thirteen, turned into a Nickleback-tier buttrock band during the 90s, have been insufferably and irredeemably shit ever since.
Anthrax - don't have any decent albums, only have a few alright songs but are overall more enjoyable to hear than the previous two, the more obvious punk-thrash influences give their music more vitality and energy that the arduous shit by Megadeth and they aren't taking themselves anywhere near as seriously as Metallica do.
Slayer - have some genuinely decent albums, good production, they only lose points for being a bit too edgy and becoming insanely derivative over their career.