I personally can't decide between V2, Piapro, and V5~ V5 has lots of neat features, but Piapro has my favorite UI. As for V2, there's just something I like about it! I like the tone the V2 and V5 editors give the vocals!
Honest to goodness that’s me but with UTAU—I’ve used other editors and find the likes of SynthV 2 to be objectively better but UTAU is my bread and butter so I will always prefer it regardless of how much better another editor is, plus I’m just more comfortable with it.But after so many years with it I'm so comfortable and used to it, and I'm very much a creature of habit, so I doubt that i'd ever prefer another editor to it even if i found it objectively better. it's just my bread and butter.
I've only used Vocaloid5 a small bit, buuuuut I am in love with all the features in there. I have no idea what I'm doing, but I know I'm having a lot of fun doing it. (I love the ornamentation stuff you can add--I haven't found the right song to use any of them, but I know I love them!)V5, all the way. I haven't been this productive and had this much fun in Vocaloid since I first got my hands on V4 back in 2018. The possibilities are endless!