I prefer both for differing reasons.
CD is good for quick research, or maybe printing out short functional checks from a number of chapters. Also IPC on CD good for p/n or search by LRU ref nos (like on the dreaded 146).
Hard copy is good for big jobs - rigging, big troubleshooting charts. Long functional checks (saves printing out 80 pages or hunting thru the FDR test for the one parameter you want to test, highlighting it, then printing it).
Hard copy also good for the 'should be somewhere in this chapter' parts hunt. Nothing beats a flick thru the manual 'til something familiar catches you eye.