I have used V4, but the first editor I bought myself was V5. I feel that they both have their own advantages and disadvantages, but I am most familiar working in V5 and find that it has more pros than cons when compared to V4. If only V5 had Job Plugins, then I could declare it the absolute winner for me.
Piapro is a good editor, but I do wish there was a standalone version outside of the DAW, like Miku Chinese/NT have. Great for when you're seeking a V4-esque experience in 2021, with V4 being almost impossible to find for a decent price these days!