I'm gonna replay Emerald. but i was wondering is there any difference between Emerald and Ruby? Or are they the same exact game
The plot is slightly different (you take on both Magma and Aqua instead of just one of the two); the available Pokemon is different; some gym designs are different; and there's more you can do, especially post-game (the Battle Frontier; catching all three weather legends, etc.).
Anyway, I may replay Sapphire for a challenge I made, and I may also replay my Emerald for fun (or do a completely different challenge on it).