What are the differences between the VoiceLive Play and the other devices?
VoiceLive Play is essentially VoiceLive 2 made simple, easy and fun (not that VoiceLive 2 is not fun to use, of course, it's just more advanced and potentially requires more of the user if you want to do fully exploit its many professional features).
Both VoiceLive 2, Touch and Play can do looping, but it's VoiceLive Touch that offers the most features in that area.If flexibility and the having as many parameters available to fine-tune and tweak are important, the VoiceLive 2 offers the most features.
All have the same high-quality Harmony processing, delays, reverbs, adaptive tone, etc. that TC-Helicon is famed for - and the sound quality is definitely on par.