We started with DCS in late 2011 and wow, so many cool features! When Legacy became available late last year, we bought that too. After 6 months of Legacy, our experience is that - we love it. It is a very robust and consistent command system. As strange as this might sound, it actually took some getting used to, given we were accustomed to DCS. Legacy is not quirky or erratic, no regular error messages, locomotives respond to all commands all the time, etc. It just works. We like the button set-up too, allowing for a better quilling effect. I must say, though, DCS has taught me to learn how to logically think through a lot of different issues, making the experience, in some ways, more satisfying. Although I can also say, sometimes trouble-free operation is preferred.
If I had to compare the two systems, I would say the DCS system is like a Ferrari - all these amazing features and an extreme level of precision and complexity, but carefree daily driving is not its strong suit. The Legacy system is more like a Toyota Camry. It has a bunch of great features, albeit not all the features of a Ferrari, but it starts every single time you turn the key and gives consistent, no-surprises carefree performance.
Overall, this is a good time to be in the O gauge hobby. So many beautiful products, so many new features (smoke effects, depleting coal loads, etc.), thanks to good competition, and two different yet similar command systems to put the hobbyist much more squarely in the engineers seat.
Peter