The Planar is much sharper, especially wide open, more contrasty, does not flare, and has a less paintery bokeh, it will also give you great colour and 3d rendering. The DR Summicron has a nice mix of roundness, good resolution and low contrast, which makes it IMHO better as a portrait lens. It definitely likes B&W, but is less suited for colour. If you shoot a lot wide open, or in colour, I'd take the Planar - for a normal B&W shooting the Summicron is inimitable.