I used FFG Mini American.
I used to be a Mayday adherent, but I can honestly say that I now feel every dollar I spent on them was wasted. (No offense, Mexsia.) FFG sleeves cost more, and you get half the sleeves per pack, but they're much better quality and they actually have quality control standards. Every pack I bought from Mayday was different. In some packs, the sleeves would be huge, leaving almost 1/8 inch clearance on either side of their cards, which would just slide right out. Other packs had such ridiculously undersized sleeves that you couldn't physically get the cards in there--they would be about 1/16th of an inch less wide than the cards they were designed to sleeve. Sometimes, I'd start sleeving with a pack and it felt good, but about halfway through the pack the sleeves started getting smaller and smaller until you just had to throw out the last 1/3 of the pack. (And don't think I was just accidentally buying the wrong sizes--we're talking the same size sleeves for the same size cards, e.g. when I sleeved new Arkham Horror expansions.) The problem seemed to get worse over time; the first packs I bought were generally good, but by the time I dropped them a couple years later they seemed to have thrown quality control out the window. And the things are so poorly-made that they'd start to split along the seams on either side after not too long.
FFG costs more, but you get what you pay for. Mayday is inconsistent and flimsy. FFG gives you standard quality.
I used to be a Mayday adherent, but I can honestly say that I now feel every dollar I spent on them was wasted. (No offense, Mexsia.) FFG sleeves cost more, and you get half the sleeves per pack, but they're much better quality and they actually have quality control standards. Every pack I bought from Mayday was different. In some packs, the sleeves would be huge, leaving almost 1/8 inch clearance on either side of their cards, which would just slide right out. Other packs had such ridiculously undersized sleeves that you couldn't physically get the cards in there--they would be about 1/16th of an inch less wide than the cards they were designed to sleeve. Sometimes, I'd start sleeving with a pack and it felt good, but about halfway through the pack the sleeves started getting smaller and smaller until you just had to throw out the last 1/3 of the pack. (And don't think I was just accidentally buying the wrong sizes--we're talking the same size sleeves for the same size cards, e.g. when I sleeved new Arkham Horror expansions.) The problem seemed to get worse over time; the first packs I bought were generally good, but by the time I dropped them a couple years later they seemed to have thrown quality control out the window. And the things are so poorly-made that they'd start to split along the seams on either side after not too long.
FFG costs more, but you get what you pay for. Mayday is inconsistent and flimsy. FFG gives you standard quality.