Awesome question, especially in sifting out brands that promote as durable but often aren't or have some products that are exceptional and others that are pretty abysmal. Most of my opinions come from working as a forester and traveling extensively around the globe to build trail.

Stuff that works:

Patagonia - Bizarrely lasts forever - I've worked in my Wanaka Down for 10 years in the woods. For whatever reason all my Patagonia stuff just lasts .

Some Filson Products - I've worked in a ton of Filson from Tin Cloth Pants to the Cruiser to all the Mackinaw stuff. Much of the brand these days isn't made for the long-haul. Filson lost some of its old-world charm and with that the overall quality went with it. Products that still hold up - Mackinaw Wool Lined Work Vest, Tin Cruiser, Field Jacket (my old one is almost 15 years old and is barely damaged), that new Wool Work Jacket. With Filson you need to really pay attention to materials, cost and rarity. The Western Worsted Wool shirt is one of the best Ive ever had in terms of durability but the more accessible shirts are expensive and nothing special, the Scout shirt is amongst the worst purchases ever.

Some Fjällräven products - Pants are repped as ultimate outdoor pants, I disagree. That G-1000 stuff falls apart pretty quick, especially considering there are a multitude of weights to it. Vidda Pro pants? Meh - Gaiter Trousers No. 1 - Amazing. Keb's are pretty good but seem cheap these days, the old cut was heavier. Their canvas down jackets are bombproof. The Numbers line is BIFL, the rest depends piece by piece.

1620 Workwear - The pants are all amazing. Double Knees have lasted forever - logged in 'em, built trail in 'em and I can still wash them and dress them up. Truly all I wear for pants anymore. I mean forever as in forever - they still look brand new after 3+ years of working on them.

Kenetrek boots - Italian made ones - amazing quality and durability.

Nicks Handmade Boots - Cool as shit and so damn solid

Red Cloud Collective - good waxed gear, takes a beating, thus far has lasted me.

Norrøna wool - The baselayers and underwear

Woolpower (Swe) - all the woolies I got from Woolpower have lasted nearly 10 years of 6 months a year wear working in the woods.

Triple Aught Design - F10 pants I've used backpacking around the world. Jeans are exceptional. Some of the synthetic stuff is just terrible and the fits are all over the place. All their technical gear is debatable in durability, sometimes customer service is exceptional, sometimes not so much. But the core of the companies clothing is what I reach for the most when Im not working. That Special Service Sweater is the shit.

Blundstone work boots - the steel toe version

Bedrock Sandals

Darn Tough Socks - Those Steely socks are the jam.

Some Carhartt - Especially the jackets have done me so well. Cheap enough to beat up but durable enough to keep on going.

Barbour - Wool Sweaters, especially the Tyne have lasted me quite a while.

I'm sure there's plenty more. Seems like many brands out there go for the durable heritage thing and don't really nail it, but there's plenty out there that does.