I think I only heard Native and Power really often than the other Voicebanks. Or at least I can't hear the difference since Gumi's voice is really powerful.
QaoQaoh
As someone who owns Megpoid Adult V4, the voice bank is ASS unless you’re an experienced tuner. Unless you want the Mellow Adult voicebank, (which is actually a really good voicebank!) I don’t recommend it.
Tamanegi-P
my favourites are native, power and softwhisper
also
idk if its just me but whisper and softwhisper both sound a bit brazilian-esque because thats how we tend to sound like here
knucklepilled
nativefat, adult, mellowadult, and naturalsweet are my fave