The precise specifications of a a reclist depends on the individual user, and the freedom that UTAU currently has is what I believe to be one of its greatest strength in comparison to other singing synthesis software. To decide on the "best reclist for everyone" is not a question that can be answered in one post, but necessitates a survey of or discussion between the entirety of the community.
That said, "VCCV English" is the name for only one reclist, which is PaintedCZ's 2015 English reclist. If you seek to eliminate the numerous variations and customizations that people have made for their own work, look no further than the original author and ensure that you keep up with information regarding their planned update.
In terms of Arpasing, you can choose to use the official computer-generated reclist, but this is the reclist that most Arpasing opponents use to define all of the method's faults. Once again, customization by individual users is the factor that brings out the strength of the method.
For English CVVC, this is a broad term that can refer to virtually every English reclist. In the interest of standardization, I recommend Delta English version 5. This will, however, ignore all independent reclist writers. Their work will not be able to reach a potential audience that may find a niche reclist to perfectly suit their needs.
Japanese reclists have less variation than English due to the nature of the language's phonology and notation, but there is still the question of what extra samples to include. A reclist that covers every essential Japanese sound is complete, yes, but what about stylistic variations in pronunciation, such as "ng" samples that replace "g"s or rolled Rs in addition standard taps? What about samples for non-Japanese words, are those essential to
what is supposed to be a Japanese-only voicebank? And common expressive samples, such as breaths and fries? For many beginning users, these samples can easily be ignored, but for advanced users, these samples are essential to their musical and stylistic goals and a voicebank wouldn't reach full potential without them.
intuitive to use for the end users.
What type of end users are we targeting? The largest factor in reclist design decisions is whether to suit voicebank developers or voicebank users. This can take a reclist to extreme opposite ends of a spectrum. A reclist meant for voicebank developers may try to reduce the number of samples recorded and the amount of configuration needed, in order to make voicebank production faster and easier to complete. But this will come at the sacrifice of usability, where, without automatic tools, will make editing USTs a very long and arduous task (for example, Japanese CVVC or Arpasing). A reclist meant for voicebank users will likely require the voicer to record and configure many more complex samples, taking up more precious disk space or OTO space and reducing the number of pitches that can be included in a single voicebank. However, it can reduce the amount of work when editing USTs, allowing the user to use fewer, longer notes, and focus more on musical tuning decisions.
In the end, I guess the reclist that wins will just be the most popular ones, and there will always be users who are frustrated with the features that are sacrificed in the name of other goals. You risk shutting out innovation.