Wouldn't it be easier to just get FF1 and 2 for the PSP?
Butting in, but this is a good question and I wrote up reviews for the lot of the FF1 games not long ago so I did a little research on this. There are usually two reasons why some prefer Origins:
1. Origins still has the charge casting system, which in it's own way ends up with the game playing differently among mages. Some say the balance went boom.
2. Orgins has a difficulty setting that GBA onward doesn't. This is because for whatever reason, Square-Enix decided to throw out the normal difficulty and just default the game forevermore into easy mode.
PSP is basically the GBA version but with better graphics, a gallery, and more new dungeons. Kind of like how the PS1 version is to NES (but with no dungeons and more bugfixes outside of the now-existing FF1 restored patch).