DAC, CD player, whatever floats your blueberry boat.
Like everything else in our hobby, it comes down to preference. Obviously a source isn't going to be completely neutral, but one can strive to have something approximating neutral. The alternative approach is seen in DACs that are marketed as being "analog sounding" or use tubes in their stages. For instance Red Wine Audio, the Havana, etc. Some people like that. I for one don't. For a few reasons:
-These types of sources tend to trade details for euphony. I'm all for euphony at times, but that can be achieved via one's amp.
-If one's source is heavily colored, then it's going to limit what you can put at the end of your chain. That's fine if you're tailoring your system to a single headphone or two. But if you want to run a diverse set of headphones, it's easier to have one neutral source and several amps of different colors (rather than several different sources).
-That way if I want a colored sound, I use a colored amp. If I want something more neutral, I use a more neutral amp. A more neutral source will in theory get along with a wider array of amps.