They are both good quality keyboard. The DAS keyboard has a glossy surface that attracts dirt while the SteelSeries have a matte surface.
Which keyboard you go with depends on what you are using it for.
Blue switch (Das Keyboard Professional) - These are the best switches for typing. The Blue switch take more force than the Brown switch, but less than the Black switches.
Black switch (SteelSeries 6Gv2) - These are good for gaming especially for FPS gaming, but they can make your fingers tired after long use because of it takes more forces to push down these keys. These are good for Counter Strike, Call of Duty, and other FPS.
Brown switch (Das Keyboard Professional Silent) - These are good all around switches that are good for both typing and gaming. You can double tap fast on these switches, so these are the best keyboard for a RTS gamer.
Edited by CocoCrunch - 10/16/11 at 12:06pm