Pete's Software is technically the best plugin, it is the most compatible, and it supports graphic features that are very complicated and/or difficult to pull off in hardware.
(though most people use pete's OpenGL/D3d or Lewpys Glide because hardware is faster and looks better)
The ePSXe's internal sound driver is reguarded by many as being the best overall SPU.
Pete's CDR 1.16 I would reguard ad being the best CDrom plugin, because it can automatically apply patches to games, and has error retrys for scratched CD's.
Liquid's answer covered it very well. But you should know that GEForce and Riva cards work best w/Pete's plugins, while Lewpy's excellent glide plugin is For Voodoo cards. So which GPU you want depends on what kind of video card you have. For SPUs, as Liquid said, everyone seems to really like the internal SPU very much. But there is another very fine SPU and that is Iori's vers. 1.46. Speech is excellent w/that one and all sounds and music are there as well. Pete's DSound Plugin is also quite good. So you have some choices to make. I hope that between Liquid and I we were able to help you.