No doubt the purple is better.
That said, the reds came out in 2012 and the purples came out in 2014. I've used the reds in true NVR without issue.
At $159.99 for a 8tb red shucked drive and $280 for a purple, I guess it's up to the user to decide it it's worth it. I'm using 4 x 8tb reds myself.