Hmm... I would have to go PSone Era, followed by PS2era, then NESera not far behind. SNESera tags the back end for me. Since I haven't really played any HD FFs... I can't really say anything about it O_o.
The reasoning for my choices would be how many from each era that I really, really liked. PSone I liked 3/3 games, PS2era I liked 2/4 (FFX-2 is my second favorite FF behind VII :D), NESera I like 1/3 games (the third one), and the SNESera I didn't really like any of the games. Now, none of the FFs are bad (well, maybe FFIV), but they aren't as amazing as some of the others.