In our opinion, there is no advantage to priming with DME. While both DME and priming sugar do not add flavor, priming with DME takes much longer. Since we cannot know the exact degree of fermentability of DME, we can’t precisely control the carbonation level of beer. On the other hand, priming sugar is much more reliable. The same ratio will get you the same level of carbonation with high consistency.
Some brewers maintain that using DME gives produces “finer” bubbles. However, this perception is largely due to the extended time required for DME to fully carbonate a bottle, which results in less CO2 in bottles during early conditioning. This causes bubbles to be smaller at first, but this will difference will gradually disapate as the DME is fully fermented and the beer is fully carbonated.