Which one sounds better to you? You might be able to buy a CD 63 for less money, if that matters to you. The 6005 is a newer model and may last longer...
I've always liked Marantz CD players. I have a CD5003 in my main system that I use as a transport only, although the internal DAC sounds pretty good. My Squeezebox and the CDP share the same outboard DAC. It's just easier that way because both units can use the same input jacks on my preamp from the DAC.