when looking at dvr cards.. it is best to use hardware compression cards H264, the clarity and quality is better also thus allowing you to use your pc for various other applications and usage.. ie it renders your system multi functional. when you ctr-alt-del and look at your performance your processor idle is running approx 20-30% unlike software compression you would idle about 80% and system performance would be a lot slower..
It is also important rather than look at the dvr card but to look closely at the software for the dvr card.. look closely at functions and features of the dvr software,, what it is capable of doing.. the pros and cons.. there are good functions on dedicated dvr units that pc based cctv systems dont have,, but likewise there are strong features that some pc based dvr cards have and are capable of doing that dedicated dvr cannot do...
I myself do prefer dvr cards especially hardware compression but ensure like pc's they can be prone to crashes and breakdowns.. however they are better managed than dedicated dvr's and especially easier to fix unlike dedicated dvr's.. good luck in your choice of system