I can't speak directly about the TD-20 but I do have a TD-8 (factory sounds leave a lot to be desired) that I use to trigger DFH Custom & Vintage samples. These samples IMO will proived far better sounding drums then any canned factory drum brain sound.
If I were just starting to look at electronic drums/samples, I'd go with something like a TD-3 (very inexpensive) and use it to trigger either DFH Superior and/or DFH custom & vintage samples. With DFH you get about 35G of samples but, you will need a fairly decent PC; especally, if you want to trigger the samples in "real-time" while actually playing live.