Do you recommend a linear or switching power supply to power the DDS?
In the past, a linear supply was greatly preferred over a switching supply because of the presence of switching transients on the dc output of the switchers. Switching supplies have made great improvements in terms of switching noise suppression over the past years. The most important consideration is adequate power supply bypassing directly at the device pins. On a side note, if you suspect a spur from a switching supply see AN-927.