First and foremonest, try both demos.
If for whatever reason you can't/won't try the demos (bandwidth caps and what not), I guess it depends a lot on what you're looking for.
-Combat is brutal. Lopping off frame limbs and performing obliteration attacks.
-Superior frame rate (~60fps for NGS2 compared to ~30fps for Bayonetta), more fluid in execution and motion
-Has online coop missions for added replayability/ the ability to play with friends
-More fluid in design due to dodge offsets. ie. You can dodge in the middle of a string and continue the string where you left off after dodging.
-More inventory management, ie. you can select two accessories, weapons assigned to arms/legs