There's no comparison. Data Illustrator gives you design freedom. I can deliver styled and beautiful viz in a fraction of the time using the data illustrator workflow. Plot.ly is going to give me standard graphs. At present you can't change the data on the fly with data illustrator (I hope that will change). I remember watching the original video of Brett Victor (
https://vimeo.com/66085662), and really wanting to work in that way...and now these guys at data illustrator are getting close to a commercial release. I think there is something deeper here than just the benefit of the design community, something that the data science community really needs....but that is a more lengthy discussion. Right now...keep up the good work!
F