I still have yet to get my first eurorack, but I have played around with most "modular" software and my favorite so far is Reaktor Blocks. Sure it is not emulating any eurorack modules, but I think it provides a professional-grade tool that is customizable and has some of the same spirit of eurorack. The best part is that you can use Reaktor to control and/or compliment a Eurorack setup.
In my opinion, VCV Rack is nice to get an idea of how a eurorack module works (provided there is an emulation of it) and could be a great option to explore new modules before actually commiting to them in your eurorack. But I would not use it as an actual musical instrument. Perhaps it'll get there one day, but that day is not today.