Also, is the only disadvantage of the PSP version over any other version that it's supposedly easier? I don't have a GBA but I have a DS though, and I could play it on PS 1 as well.
Yes. I have DoS, and that version is pretty easy (even a run with a solo thief wasnīt hard) and some people say that the PSP version is easier, but the PSP graphics are awesome.

Anyway, I still play the NES version, which is my favorite (I have only played the NES version twice, but itīs still my favorite)

I could play it on PS 1 as well.
If that means that you have FF Origins then try that version on normal mode (I have heard that normal mode should be the same difficult as the original NES version)