I use both Dragon Shield and Ultra-Pro.
But have there been any quality control tests that show statistically one brand is more reliable than the others?
I have not seen any independent quality assurance tests comparing the various sleeves, and I sincerely doubt there is a comprehensive one to be found. It's probably not economical for anyone involved, since QA comparisons like that can be quite expensive.
From anecdotal evidence at my local shop, which has ~80 player FNMs every week, most players seem to agree agree that:
These are the three most popular sleeve types at the shop.
I haven't seen any QC tests but I have been using both over the past year. I have every color of Dragon Shields (except Brown and Pink) and I have only had an issue with 1 set (some tearing on about 10 sleeves). I double sleeve my cards using Perfect Fits on the inside and I riffle shuffle. that puts a ton of stress on the sleeves
Ultra Pros are good, not as thick as Dragon Shields, but I haven't had an issue with them. However, I've seen many of an opponent tear an Ultra Pro midgame.
I always put it to my friends this way... In the lifetime of a box of sleeves you can buy one box of Dragon Shields or 3 boxes of something else.