Gosh... well...the following is as I understood things. So take it more as an opinion:
Early on, I always used Mustad, bc that was the best hook out there. At one point I sent some trolling flies to China with a friend to see if they could be produced there. The reply was: They could duplicate everything but the Mustad hooks bc they didn't have that quality steel at the time.
I've had some poor lots of very early Mustads though -94840's that weren't tempered right. But for the most part Mustad's were just fine.
When the Japanese hooks came in though, a notably better quality hook, things changed at Mustad too and they began to offer newer lines of hooks offering new competitive designs and most importantly higher carbon steel. These cost a bit more than the old standards, but not as high as the Japanese ones. Part of that cost I always assumed is the strength of the Yen and cost of living in Japan, but also in R&D bc the Japanese took the market by its shirt collar, like they did to the automobile industry.
I remember the first Gamakatsu hooks I ever saw (in the mid 1980's) and was shocked at the price! "Who would pay that much for hooks??" I thought. But over time, I got to see the qualities they offered: high carbon steel (which means a stronger hook per weight, remain sharp longer, and can be re-sharpened longer), sharpness out of the box, and consistency in these qualities, as well as some designs I could not get in Mustad -at least early on.
Now, these qualities were most noticeable (glaringly so against some Mustads at the time) in larger hooks such as bass fishing hooks (for softbaits and hardbaits), and saltwater fly hooks. With comparatively tiny trout hooks, the difference wasn't so obvious, being thin enough to get hooksets easily enough. However, with the original Mustads, and heavier wire ones esp, I sharpen often on the stream. Most people don't pay attention to hook point sharpness. For me, my hooks must stick into my thumbnail and not slide. This is critical with large fish like bass and SW species. It's also important for trout, although one can get away with more bc of the soft mouths and comparatively fine wire hooks used. But I sharpen my fly hooks as I fish.
For fly-tying, Mustad is what I have the most of. I use both their older styles and their "newer" ones too. I also use the Japanese hooks too, as well as some very high quality Sprite hooks from the UK (which I don't think are made anymore). And I use the Eagle Claw L42 for some egg flies.
Guess that's what I have to say about that.