First, a quick disclaimer: I own multiple boxes of Dragon Shield sleeves purchased at different times, so I can quite reasonably attest to their quality. However, I only own one pack of Ultra Pro, so my initial judgement may be from an odd pack and far from the norm.
With that out of the way, here's my opinion:
Dragon Shield all the way. A relative bought me a pack of Ultra Pro sleeves once (I had only ever used Dragon Shield until then) and that gave me a great
opportunity for side-by-side comparison. I even did that test where you grab the open edges and pull as hard as you can, trying to break them. Here's my comparison:
SHUFFLING:While Dragon Shield was smooth and delightful, the Ultra Pro sleeves seemed to stick the cards together in chunks while shuffling. There seems to be some kind of static
charge generated by the texture of the Ultra Pro polymer that holds the sleeves together so that they don't "whoosh" off of each other in a clean sliding fashion. I think that the texturing on the back of the Dragon Shield sleeves gets around this (I use basic sleeves, not the art series which has no texturing).
Another note: It is very hard to "mash shuffle" with the pack of Ultra Pro sleeves I got, due to the same sticking sensation and the thinner edges of the sleeves that refuse to seperate from each other easily. This is probably not the norm.
HAND FEEL:Both feel pretty nice in the hand. I can't deduct any points from Ultra Pro here, because there is no problem with how they feel in hand. However, the Dragon Shield are just exceptional. The texturing on the back makes it easy to hold them while stopping them from slipping away from the others.
LOOK:Something you might not see in the pictures or the advertisements is that the Ultra Pro sleeves tend to have a slight matte finish on the front while the Dragon Shield has a clear, glossy one. Just different plastics, I guess. I would say that Dragon Shield was superior here, since the cards (especially foils) definitely look better. However, the problem with the gloss sheen is that bright lighting can cause glare. The Ultra Pro sleeves sacrifice a little bit of foil shiney-ness for a little bit of practicality, and that's fine.
SCRATCH RESISTANCE:The aforementioned finishes on the fronts of the sleeves are the main factor in play here. In short, the Ultra Pro sleeves are scratched more easily and show scratches more prominently. The Dragon Shield sleeves, while still scratchable, hide the scratches unless angled under bright lighting at specific angles. Dragon Shield wins here.
STRENGTH:Even though we don't grab our sleeves and
attempt to rip them apart, I thought it would be fun to test anyway - especially since you always get a couple extra sleeves in a pack. So I did! I pulled as hard as I could on Dragon Shield and either I'm weak or the sleeve is unnecessarily strong, because it did not break. However, the sleeve was rendered unusable due to stretching. The Ultra Pro snapped at about 75% pulling force. Still far above what is practically needed, but once again, Dragon Shield wins this category.
WEAR & TEAR:None of my Ultra Pro sleeves have broken due to normal play. This is probably mainly because they are very hard to abuse (see the note under shuffling). I have broken 3 Dragon Shield sleeves while "Mash Shuffling", all in the same deck, so it might have just been that one box. I can't say for sure that Ultra Pro wins here, since only sleeves from one specific pack broke, after a year of punishment. But then again, this isn't exactly an accurate comparison, since Ultra Pro only has a sample size of 1. So it's hard to say!
Anyway, that's my comparison. I always buy Dragon Shield now. Ultra Pro is certainly not bad, but I feel that Dragon Shield has proven itself superior. Others might have different opinions