There are significant objective criteria as to which emulator is the most complete. It's called their game compatibility list. If emulator A plays 95% of games, and emulator B plays 80% of games, then emulator A is more complete than emulator A.
Example: PCSX plays pretty much everything, pSX plays rather less and ePSXe needs configuration for a significant number of games. Conclusion: PCSX is the most complete.
"Best" is more difficult as it takes into account things like emulation speed etc. as well as all the usual problems with quantifying best. For a emulator of really old systems on any modern PC though, speed is irrelevant therefore "Best" can still be taken as most complete IMO. To go back to the PS1 example: PCSX is objectively the most complete, but "best" could be about the debugging features or plugins available. Therefore "most complete" questions are not the same as "best" questions.
The complaint that answers are likely to change over time is a non-issue for most platforms. Where stable emulators exist, the pace of change is glacial. Should we ban Terraria or Minecraft questions? They're more likely to change than emulators.
Merging all the questions into one with links to emulator information is just downright stupid. The answer to "What PS1 emulator is the most complete?" is different to "What N64 emulator is the most complete?". Merging them into "Where can I find links to emulators" is like merging all Dwarf Fortress questions into "Where can I find information on Dwarf Fortress" and linking to the Magmawiki. We are a question and answer site, not a forum of links to FAQS.
As to Strixvaria's complaint that all answers are equally valid: This only applies to certain consoles, such as the gameboy which are simple enough to have hordes of emulators written for them. More complex consoles have fewer emulators with more difference between their compatibility. Nearly all boss fight/strategy questions will. If more than one emulator has 100% compatibility, answer with a list. X and Y are both 100% complete.