I'm not sure what makes shell X better than shell Y.
Once upon a time there was a poster on Dennis' forum who was always banging on about shell makers taking the P producing crap shells because we're all so gullible, and how he was the voice in the wilderness trying to save shooters from wicked shell companies blah blah blah. I think his forum name was IASGAIR or something. Mr Angry would have been more approriate.
Let's be honest, most of us buy the bangers that we get an acceptable local deal on. I'm not interested in driving 200 miles to buy a supposedly wondrous shell when no-one thus far has explained why exactly it's better. As for the internationals, I daresay they do much the same in the sense that they'll use whichever maker offers the best financial incentive.
About 10 years ago I bought 1,000 Fiocchis, Top One I think, and they were hilarious. I had flames out of the barrels, nasty recoil, very noisy and the barrels ended up blacker inside than out. I went back to the dealer and argued successfully to replace them with something more user friendly. Hopefully they're a bit better these days.
I've used Blues and Olympics and, through extensive testing, proved conclusively that they're not the same colour. Express, Gamebore and Hull seem to break clays too and I'd say it's a fair bet that Clever & Fiocchi will also break them. Actually I've never yet come across a shell that doesn't break the clay when I stick the gun in the right place.