I have the leather loop for my sport. I don't wear it much, a little too hot during the summer here in Florida. But I like the way it looks, really cool. I tried the classic buckle in the Apple Store and it too feels really nice.
I have a third party leather loop knockoff (black) that I wore with my aluminum Sport most of the Winter. If it's not hot, it's my most comfortable strap. If it is hot and humid, then it gets really funky really fast. Being infinitely adjustable you can always loosen it up, but that doesn't seem to help too much.
During the warmer months I wear a brown leather Clockwork Synergy buckle that I usually wear a little loose. It's fine for our cooler Summers in the Pacific NW, but I grew up in the South and was visiting family this Summer. I wore the Sport band almost exclusively because of the heat and the humidity. The Sport band isn't exactly cool, but you can clean it more easily than the leather loop.
This Summer has made me long for either a Milanese loop or a woven nylon... I hear both of those are lighter and more comfortable in hot weather. I would imagine the Milanese Loop would be the coolest. I have been eyeballing a few third party ones on Amazon that sell for between $10 and $20. I'm not sure which would look best with the aluminum Sport. The stainless steel ML wouldn't quite match. Black might look good, but they also offer a space grey that might go well with the aluminum sport case.
Has anyone found a brushed/aluminum finish Milanese Loop?
Sean