I ride with Diesel's and Naked and Famous. The diesels are so comfortable, even tighter ones are good to ride with. And they last me a long time.

Agreed 100%.

I was recently introduced to Diesel and they are the best in terms of fit and comfort. I particularly love their JoggJeans.

They are a little pricey but so worth it

Spoke make a pair of chinos-ish specifically reinforced (and zip pocketed, and semi-waterproof) for cycling.

I haven't actually tried them, and I no longer commute, but I used to burn through the seat (and more one side than the other, interestingly - probably says something (bad) about my cycling technique) the same way.

Could simply be a fit problem. Check out pants with larger room in the thighs and maybe even a crotch gusset.

I had a pair of Levi’s Commuter Pro that were 5 years old (with a lot of wears and washes) and still going strong before I lost them :(

Somehow it seems like they’re now discontinued.

I loved the commuter line. The first run of them were absolutely perfect. But, as with many things Levi's, they started using cheaper and cheaper materials over time to the point where they were just unwearable.

(If anyone at Levi's is reading this, for Pete's sake, stop cannibalizing your own brands!)

Levi’s used to have a Commuter 511 model designed for cycling. It had reinforced panels in the crotch where the bike seat goes, reflective Scotchlite piping on the seam where selvedge would normally go. They discontinued them AFAIK but you might be able to find secondhand.

The commuter line was fantastic, I would love to know if any brands has a modern equivalent.

Not jeans, but I love Prana shorts for riding. I have several pair that have lasted several thousand miles each.

Not true jeans, and you'll pay for the durability, but Outlier comes up occasionally amongst bike commuters. I wore my strong dungarees (now replaced with bomb dungarees but different fit and material) to bike to dinner dates many times. The new way shorts aren't quite as durable but I wore them biking a lot too.

I actually prefer to buy my Outlier pants secondhand (at a significant discount, mind you) because I’ve had such good luck with their durability.

Unbranded for “cheap” quality denim, Iron Heart for high end. In general the higher the weight of the denim the longer it’ll last. 21oz denim will last a very long time.