When I had my FM3, I spent a fair bit of time comparing the pitch shifting on the FM3 vs the Poly Capo on the Helix.
My conclusion at the time was definitely that the Poly Capo tracked better and had less artifacts, but at the expense of using a huge amount of DSP - fine on the Helix, less so on the HX Stomp.
When I had my FM9, I didn't even try the pitch shifting, but to my understanding the FM9 got the new pitch block from the AxeFX III, which was supposedly quite a bit better - I should really try it on my VP4, but I've no idea which version of the pitch block the VP4 has.
As to opinions - there are loads of people who will swear that the QCs pitch shifting is better than the Poly Capo, when it isn't even polyphonic, and has very audible artifacts if you play any sort of clean tone, but are masked somewhat by gain - I broke out my Nano Cortex recently and whilst I'd say it has improved a little from when I had my QC, it still isn't great.