Where the heck would you get a CRT monitor that takes a DVI input (other than maybe an HDTV)? DVI is a digital output standard, and CRTs are analog displays.
For something like an HDTV that *could* take DVI or VGA, I would recommend DVI -- the digital signal is more immune to electrical interference and noise, and odds are the RAMDAC in the TV is better set up for that particular display than the one in your video card. But the differences are going to be minor at best.