There is no such thing as 'the best plugin'. How good the plugin performs is highly dependant on the system it runs on and the games you want to play.
The plugin that performs best for me might perform the worst for you and the plugin that performs best for game A might not even run game B. Only if you have a voodoo graphics card you can safely say that Glide64 is by far the best plugin for that specific system.
Greetings and good luck testing,
TRS