Admittedly, I have not used a whole lot of different card sleeves. But I can say that these are an incredible value compared to most. If you're a board gamer and using them for that purpose (as I am) you know that often, the cost of the "higher end" sleeves can outweigh the cost of simply replacing a game's card set when they get worn/damaged, making it a waste to invest in the sleeves. These, on the other hand, are incredibly affordable and therefore well worth the investment.
The other things that I really like about these sleeves:
1) They are thin, meaning that your card set doesn't physically "bulk up" a tremendous amount. When some games can contain 200 cards or more in the set, the thickness of any sleeves really does add up quickly, often rendering the box/storage of the original game unusable
2) the "slipperiness" of the sleeves make your cards really pleasant to shuffle (which there can be a lot of in modern board games)
3) after using over 1500 of these sleeves (Pathfinder ACG, LotR LCG, Dead of Winter, Last Night on Earth, Pandemic, etc), I've had literally ONE bad sleeve that I can recall (somehow it was folded up on itself). I DID have one bag (they come in ten bags of 100) where a number of the sleeves were a bit tough to open/stuck together initially, but it was maybe 20-30 sleeves total
On the negative (as has been suggested by some): if suppose that if your cards are going to get really heavy play (or you're just particularly tough on your cards) these may be too light for you. Or, if you're looking to protect really valuable collector cards (sports card and such) you might want a heavier sleeve. Otherwise, I don't know how you go wrong with these Ultra Pro "penny" sleeves---highly recommend!
Manuel
Mimi Sasek