I think in terms of "how easy it is to make them sound realistic", from the ones I've worked with my picks would be Yamine Renri, Mawarine Shuu, various Kohaku Merry voicebanks, Anna Nyui's vivid bank, Number Bronze, Akesato, Koharune Ami, Karashine Akito, Zuiga Mizuki, and... most of the...