I love Audioholic's common-sense approach. This is the Jack of all trades site. Where you can discuss objective, subjective, high-end, budget, vintage, cutting edge, the whole works... well except for extravagant cables. Those might get you a slap.
Audiokarma is like someone else said, obsessed with goodwill store deals and vintage gear. Fine in itself, but any questions I asked there got no replies. I quit posting after getting reamed by a long-timer when I only commented that a pair of speakers I bought over 20 years ago sold for more now than when I bought them new. The attitude was more or less "of course, dumbass!" Yeah screw that place. You'd not think people who thrive off paying $30 for equipment would be snobs, but...
Audiogon is a special case. It's the worst place on earth to go for advice. It's all snake oil over there. Magical copper discs on the wall (I really should buy a penny squasher). Magical quantum fuses. Magical cable elevators. The core philosophy is "if it costs 10x more it sounds 10x better." In their minds price and sound quality have a linear relationship and diminishing returns don't exist. So why bother? Well you skip the forums and use the classifieds! Man those guys LOVE taking huge losses selling their stuff! The best thing about the "more money than sense" crowd is that when they want the new shiny they get in a mad rush to get rid of the old shiny. You can get Bentley equipment for Kia prices on that site. So do your research on a sensible site then buy it from a millionaire retiree who just wants it out of his house.
I just recently joined Audio Science Review after lurking for over a year. That's a fun place because it's the bane of all the subjective bullsh1t sites on the internet. Nothing gets posters at head-fi, stereophile, or Reddit audiophile boards more riled up than a link to ASR. It's actually hilarious! Nothing fires up that crowd like being told "your super expensive gear is highly distorted and non-linear." The usual retort is "I don't care how it measures! It sounds better (
because I took out a second mortgage for it)!"
TLDR, the internet is a funny place.