Bates are leather. Wintec is synthetic. BTW - I have two Bates Caprillis that are sitting in my den unused. If you could use a 17.5" CC saddle, or an 18" AP saddle, send me a PM.
FWIW - I like the leather on the Bates. The interchangeable gullets are interchangeable, but it isn't something you want to do often. I changed mine once for a different horse, and once as the new horse changed size a little. I usually end up cussing a lot when changing the gullets. They must hire actors to smile in the Bates ads.
Bates has CAIR, Some people like it. I do not. My horses like it fine & they move well with the saddles, but I would prefer a flocked saddle. I suspect a lot comes down to individual taste and the shape of your horse. My AP saddle is flatter on the bottom than my CC saddle, although they are both Bates Caprilli saddles. Go figure...
I ended up drifting into using an Australian-style stock saddle, and there is a good chance I'll keep using them. They make more sense for how I ride (which is marginally!) and my horses (a bit spooky!). I tried riding in the AP saddle yesterday for the first time in 6 months, and felt really weird.
If at all possible, sit in the type of saddle you are thinking about before you buy. If you buy without seeing the saddle, you are taking a chance. If you buy new, make sure you know what their return program is.