I've owned mugen, xray, Durango, losi, and serpent. They quality of parts of the serpent is of xray quality, but the fit and instructions are under par. Like all kits, serpent has their issues. In regards of setup, it seems that chad setup is pretty bullet proof. The drive of the serpent is one of the best buggies I have ever driven, if not the best. Like folks have said, the serpent requires experience. Reason being is due to horrible/incorrect instructions. If the instructions had more details without any errors, this buggy would be more user friendly to the avg Jo blow.
I never owned a kyosho, but my friend has one. The drive on this car is on par with the serpent. Looking at the parts, you will get more upgrades with the kyosho.
The serpent would require more work. But once it's done, it's great on the track.