USB stuff and DDC can't be directly compared because they work in different ways.
With USB, your DAC is completely in charge of timing. There is no clock signal for audio on USB, and in fact it's a two way communication, the DAC itself asks the computer/source for more data when it needs it, and converts according to the timing dictated by its internal clock.
For this reason, with USB the only thing you need to worry about is noise, which an Intona completely addresses in that it both blocks all noise from the source, AND is incredibly low noise in and of itself.
USB 'reclockers' simply cannot provide any improvement in jitter/timing, it does not work that way and no one has ever demonstrated an improvement in jitter via the use of a USB reclocker.
DDCs that output I2S/AES/SPDIF are different because whilst they also seek to provide a very low noise source, they DO provide a clock signal to the DAC. This clock signal is what the DAC uses to determine when to convert samples and so the timing accuracy of the clock signal provided by the DDC measurably affects the performance of the DAC even though the data itself has not changed.
As to whether a DDC or using USB is better, it depends. A few years ago I would have said definitely a DDC, as many DACs simply didn't have very good USB implementations/internal clocking and so there were quite significant improvements to be had by using a high performance I2S DDC instead.
Nowadays though, many DACs even at lower pricepoints have exceptional jitter performance and it's a lot rarer that a DDC will actually improve things. In fact in many cases they may make it slightly worse. Though most good DDCs do also provide galvanic isolation so again blocking noise from the source is a benefit.
My default recommendation nowadays would be to get an intona, they make a cheaper USB 2.0 only variant as well, though the 7055-C is the lowest noise one if you want the best performance (also looks the best IMO).
