SA-MP files: Very slow and difficult.
Dini: Slow but easy.
Y_Ini: Fast and easy.
MySQL: Very fast, not intricacy but difficult and need PHP knowledge (low but need).
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If u want write a GM RP but you want export the players data on an online DB, you can do this also with Y_Ini and Dini, but it is a bit more difficult than MySQL, because the Y_INi/Dini/Files are file system, instead MySQL is a database.
My GM is very good (I'm at 4000 lines) and I writed it in Y_Ini, at the beginning is difficult to learn the Y_Ini File System, because it is very different from the others file systems, but you will find it very simple in the end!
I'm sorry for english errors, but I'm italian and I can't write well in english