I've just bought the same bag myself today () so I don't have first hand experience but from what I've read on this forum and from my friend who has one, the softer leathers get so slouchy that they end up a puddle while the polished buffalo does relax a bit but still keeps its shape.
Would love to hear thoughts from someone who has had one for a while!
Yes it does slouch a bit. I own a midnight one and I also think the leather retains that new look for longer. Buy one, I don't think you'll regret it. If you click on my profile you will find a picture of the midnight and see what it looks like on a chair.
I have a newer one in polished leather and an older one in the softer leather. Sorry I forgot the name. The polished leather one is indeed very stiff, even after years of usage. I would say mine is still pretty structured now, and holds the shape as new. It is completely different from the older one, which is very very slouchy that it can't stand on its own. I love them both. They are just different.