ePSXe is just more popular. PSXeven isn't inferior. ePSXe achieved a very compatible state before PSXeven and PCSX, but that doesn't mean both are inferior than ePSXe. As a matter of fact, many games work on them better than ePSXe ( take Xenogears for example, PCSX runs it flawlessly - except for the common 1st Dues battle bug ).
ePSXe gets more use because it just snowballed. i started using it becuase a friend told me to use it, and i mean look at the boards. there are many for ePSXe...and barely any for PSXeven. still, PSXeven is totally great and so is PCSX. either of the three are perfectly fine to use. and remember, if you have problems, just switch
yup; it's more known and therefore more popular, because at the time when it came out it made quite an impact; psxeven arrived much later and stuff but then I found out I actually had slightly better results with PSXeven.
yep psxeven does seem to be better a touch more than epsxe. maybe because psxeven addressed different problems than epsxe in its newer versions. nevertheless, i still think epsxe is dominant and will be for a while if it keeps alive
afaik, Crisis Beat, Incredible Crisis, Some parodius game (forgot which one) and Viewpoint work better in PSXeven then they do in ePSXe for example. I peronally don't know about games that work better in ePSXe, but I'm quite sure there are; I just don't happen to have (played) them.