Looking back, I've never had a bad primer from Winchester, CCI, or Remington. But only did 1k of Remington and several K of the first two. Not being a benchrest shooter, I can't tell you which ones are more accurate. So between Winchester and CCI, here's my take on the trivial differences I've noticed between these two (that amount to nearly nothing):
Esthetics:
CCI: Primers are bright silver.
Winchester: Primers look like they're corroded, right out of the box.
+1 to CCI
Packaging:
CCI: A little more compact, and the cardboard looks new.
Winchester: looks like it was printed on recycled cardboard with a press from the 1960's.
+1 CCI, if you're a packrat with limited storage space. +1 Winchester if you're a treehugger.
Packaging 2:
CCI: 3-20 primers per tray are flipped upside down
Winchester: 99.9% of the time all primers are right side up
+1 Winchester
Primer markings:
CCI: all CCI SPP and SRP look exactly the same
Winchester: each primer is color coded on the top of the anvil.
+2 Winchester. This is the only manufacturer I know of that does this. It's great, esp if you occasionally substitute regular/magnum/rifle/pistol between each other and prime your cases in advance. If you have any doubt, you can shine a flashlight into the case to see which primer is in there. Or if you have a lot of assembled ammo sitting on a dusty shelf with no label, you can pull one bullet and look in the case.
Other: I've run 1k of CCI SRP through my Glocks with zero light strikes. Never tried that with Winchester. So +1 for CCI SRP, for the versatility.
Price:
Right now, at Powder Valley, CCI are 26/k for SPP and SRP. Winchester are 25/k for the same. That's pretty much a wash. Federals are also the same price, so I might finally give them a try.