You can get a good overview on the Pit Page at http://www.kingsnake.com/pituophis/p_m_lodingi.html.
I've kept milk and kingsnakes but I haven't kept a black kingsnake, so I can't compare them to a black pine from personal experience. I can say that black pines are good looking "in person". Although their scales are keeled, they're surprisingly glossy (before I got one, I thought they'd be flat black). Black pines are a good size (heavier in build than kings) and are good eaters.
I saw your post in the milksnake forum and I'd agree with what Greg said. The thing I like about black pines is their personality. They're NOT boring. They've got their moods and communicate them well. They vary in personality too, although most are a pleasure to own. My black pine is usually very docile (never bitten me) and she's entertaining... active, interested in what's going on around her, and those times when she wants to be left alone, her hiss lets everyone in the house know it! All the glossy black snakes you mentioned are beautiful animals but, with black pines, you can add personality to that beauty.
) I've talked with folks about indigos (which started the whole idea of black snakes), blak milk snakes, black king snakes, black rat snakes....and then black pines were brought to my attention. I've always thought pines were interesting snakes.
