I like both games. NHL 06 has great graphics, and is definitly not the sim game. I see what SDM is saying. Players like Jagr and even Kovalev are almost impossible to stop. Seriously, Kovalev is not a 50 goal scorer.
I find it really fun though, especially with a group of friends. If you only have a PC, it's the only hockey game out there (unless you want uber-sim Eastside Hockey Manager).
Of course, if you have a console, NHL 2K6 is the game for you if you want realism. The fact that you can actually cycle the puck on the powerplay alone is worth the price of admission. The only gay thing in the scoring exploit, but on Hall Of Fame is tough as balls to pull off, and I never use it.