My all-time favorite black bag ever is my Marc Jacobs black quilted Stam. Its hard to beat, classic and timeless.....
...but for your favorite, being a slouchy hobo with awesome leather, I'd say a Rebecca Minkoff Black Nikki (you can find them for reasonable prices on eBay or bonanzle), or the Balenciaga Black Day hobo (much higher price point, but an excellent bag!!!!)