If it was my opinion; Kaito, we have so many female vocals and most of CFM's vocals no longe are special. Meiko and the Kagamines are nothing special anymore and are common vocal types, meanwhile theres just better vocalists in every way at singing then Miku, and Luka's V4x wasn't anything special, despite what Luka fans claim. As a male vocal, Kaito doesn't have many rivals and opposing vocals to challenge him, so, he just ends up being the best as a singer.
If is based on technicalities... Miku V4x is about the best package you can get in terms of Japanese CFM voicebanks... And with both English and Chinese, its kidna a no-win situation. The weakest bit of Miku is the laughable Miku NT release, I'm thinking Miku should have stuck to Vocaloid and not left. At this rate CFM would be better turning for V6 or V7.
I feel these polls aren't particularly anything speical, we've discuss CFM to death and their no longer with Vocaloid so... unless they return, there will in 15 years time or so be a era where non-Voclaoid CFM vocals overtake Vocaloid CFM vocals.