No one in their right mind could deny, that RetroArch is the best type of its application around, from the sheer number of cores that we have access to, to the dedicated devs the team has, this software just keeps getting better and better, from starting life on the PS3, to being on almost every device imaginable, to finally today coming to the PSP.
Do note that it is a beta and will not have the same amount of cores as it does on pother devices, but that will improve over time, here is a quote from the source:
currently contains following cores :
more cores may be added in the future if they prove to be fast/stable enough to run on the PSP.
bios files go into the cores/system directory..
for psp slim/go, make sure you disable iso cache, and enable high memory layout to allow acces to the extra 32MB ram. (can be changed from your cfw menu ).