The trouble with Levi's is that when you buy, say, a pair of 501s, there are a bunch of things that factor into what you're getting. Bought them on eBay for a good deal? Solid chance they're counterfeit. Bought them at WalMart or Target? You're getting a variant that was manufactured for downmarket, price-sensitive consumers - thinner denim, cheaper manufacturing. Is it stretch denim, or 100% cotton? Shrink to fit? Levi's Premium? Or maybe you're splurging for something from the Made & Crafted line. Or if you're really looking to spend on Levi's, you've bought something from the Levi's Vintage Clothing line. (In the US, you can still sometimes find LVC and Made & Crafted items at TJ Maxx and Marshalls for a tenth of their retail price) Sometimes the fit is inconsistent, but if you buy from levi.com, you get free returns if you have an account with them, or if you can drop them off at a nearby Levi's store.
And that's just Levi's... I don't have the time or the energy to bother with the kind of denim fanaticism that blew up over the last decade or so.
Before they IPO'd, my trick to long-lasting Levi's was to wait until whatever seasonal collection they had with 'toughness' in mind went on sale or blowout, because they used to experiment more with fabrics. I've got a pair of 501s made with Dyneema, the stuff they make ropes for ships out of. The Skateboard line was marketed as being able to take more abuse than normal, and so far has lived up to that. For better or for worse, they've simplified their product line a lot since being publicly traded.
And if you want to get real weird, the other thing that I found helps is... that's right, not washing my jeans every time I wear them. There are exceptions, but I work from home, I'm generally not doing much to stink up my jeans. I have a rolling rack that I keep 10 pairs of jeans on, and I cycle through them, so that at the very most, any pair gets worn once every week and a half.
Anyway... I haven't had to buy new jeans in a long time, and I switched over to all-Levi's years ago - but It took a little trial and error to get a lay of the land.