It depends on how you use them and what your budget is.
I've had good luck with a moderately priced e-kit, using it as a MIDI controller to drive drum sampler software like EZDrummer and Steven Slate Drums. In this case, the e-kit doesn't provide the audio, just the MIDI data, and the sampler software provides the actual sounds. So the kit sounds as good as the sampling software.
You can also record the audio output of an e-kit's "brain" or control module. It's less flexible, but if your kit has good-sounding samples built-in, then you don't have to fork out more cash for software on top of the cost of the kit itself.