VCV rack is pretty awesome, and you can do a lot of things with it that you couldn't with Zupiter. It's much more of a professional tool and as far as I know it's very well-regarded in the modular synth community, and a good way to pick out modules before spending hundreds or even thousands on physical hardware.

However, I think Zupiter is a nice way to get people who've never played with sound synthesis interested, and the sharing feature is one thing that differentiates it from most browser-based music apps out there. You can easily show your friends what you've made, or modify what other people made.