The DCS system is very good. It has quirks like every other. The frequency it uses was common at the time, doesn't make it a copy 9f NCE. But, both Lionel and DCS are falling behind what DCC is doing now. DCC has its limitations too though.
As for Railpro they have a great sound selection for diesel but are limited in steam. Tim Ring told me via email his is working on that right now though. The sounds I have heard are excellent and you can add your own custom sounds.
There are no perfect systems and everything is a trade off in some area. However if you use DCC you can get decoders and sounds for any scale and any loco. Railpro serves HO through G and is working on N. DCS is O and MTH HO only. Depends on your wants and needs.