the pussy 9mm
for rifles, it's 5.56 easy. 5.56 in a 20" barrel is good but when you go to short it becomes a pussy like the 9mm.
for bolt guns a ton of guys still use .308 and 30-06. I prefer magnums. 300 Win mag is still very popular and you see 7mm Rem mag brass pretty often at the range too.
In general the gun community sucks now like everything else. You have a handful of shitty or boring calibers and nothing else anymore. Gone are the 44 magnum and 357 magnum enthusiasts. No one shoots big handguns anymore. You used to have die hard guys around 44 magnum, 454 Casull, and definitely 357 magnum but not anymore. You really don't even see 38 special or 45 Colt shooters anymore. 10mm became a big meme as of late but no one shoots them because people are too stupid to figure out how to reload to get around the cost of ammo, plus we don't have any really good 10mm guns, just a few plastic 9mm guns retconned with heavier springs and 1911 10mms which are universally awful guns.
There are a ton of great calibers out there that dramatically outperform the 9mm and .308/30-06/5.56 trifecta but they are hyper fringe now because the dumbshit public is too dumbed down and stupid to figure out how guns work, let alone actually caring about their guns enough to force manufacturers to expand their lineups. Everything has been tacticool'ed.