Top three used to be Meso, Brotherhood and Evolutionary. Probably still are, and maybe ASF. None of em really offer anything different; Gear is gear. Tren from one lab is the same exact drug as Tren from another, Dbol is Dbol, etc as long as the sources are actually putting the claimed drug and dose into the pill/vial it's not going to be noticeably different whether you ordered from Lock and Load or Hunter or TM or Bobs Burger Labs or Yo Momma So Fat Labs etc get the idea?
The only real difference in other forums is the community they attract. Meso attracts people like me (Assholes, realists, logical people), Brotherhood attracts antisocial people (Seriously there's hardly any activity there.....), Evolutionary attracts Dylan Gemeli's SARM goblins (Retards, Tiktokers), ASF attracts the guys you find at Westside Barbell 20 years ago but now they're 20 years older and just trying to keep up with father time.
SST to me feels like /pol/ mixed with oldschool Reddit (before it was all retarded trannies and BBC enthusiasts) in the sense that we have some very intelligent minds here and a lot of fun threads full of actual solid info and good laughs while also not taking shit too seriously. Unlike other boards where people are more open about posting pictures (which feels sketchy as fuck to do for USA folks) to try to aid their point, SST posters pretty much earn their merit through just pure informative posting. It's less "Hey listen to me because I found this picture on Google of a jacked guy to post" and more of people actually detailing experiences and methods which others will find, if they take the advice, work incredibly well. If you spend all your time listening to what the guys on Meso or Evolutionary say works, you will end up sinking thousands of dollars into gear and look like fat bloated shit or weak scrawny shit. Here, it's more of a 'Money talks, bullshit walks' place where longtime members absolutely push back hard against retarded nonsense that gets posted so nobody falls into the trap of being retarded as well.