I own both. I have a Mini Sasha in Black Patent, and a Silverlake in Dark Amber. I actually feel the Silverlake is a good deal because the braided handles fall more naturally on the sides when carried as a hobo. The sasha handles are quite stiff, but I think it might be that the patent leather is more rigid than lamb leather.
Another thing that I like about the silverlake is that its zippers open and close more smoothly than the Botkier Sasha. I also own a Medium Bianca in Bronze, and both zippers are kind of hard to open and close. With the silverlake, I can open and close the zippers with one hand, even when I am driving.
However, I still can't deny that Botkier has better leather quality. I don't really mind that the Silverlake from The Sak is a copy cat, I buy all sorts of bags, expensive ones and inexpensive ones. I collect expensive bags, but I buy inexpensive bags to be my everyday bag, so I don't need to worry about damaging it, and when it comes time to give it away, it wouldn't hurt as much as with an expensive bag.
I would categorize Botkier bags as my collection bag, and Silverlake as my everyday bag.