Emerald >> RS > FR/LG
I have to vote for RSE, even if Red was the first Pokemon game I have ever played.
In my opinion, Red/Blue lack of story, yeah there's TR, but not much is known of their goals/history/etc. Ands FR/LG haven't really improved that part.... I prefer when they're tons of sidequest (by sidequest I mean everything that isn't getting badge and beating elite 4 & Champion).
The only let down of Emerald is the lack of some previous gen Pokemon that were liked by players (like eeveelution/Gengar/etc.) But it bring out couple of really nice new Pokemon too