Sell your Sapphire and buy Emerald. I am not joking. There is no comparison between Emerald and Ruby/Sapphire. Emerald has everything RS has, and A LOT more. Here are a few of the changes that I can remember off the top of my head:
- All Pokemon sprites are now animated
- Some Abilities can now be used outside of battle. (i.e. Arena Trap increases encounter rate, Sychronize increases the chance a wild Pokemon will have the same nature, Flame Body decreases (almost in half) the amount of steps needed to hatch an egg, etc.)
- The Pick Up Ability now changes items you get depending on the level of the Pokemon (i.e. Lv91 Pokemon has a 5% chance of getting TM26 Earthquake)
- PokeNav now has Match Call, where trainers (including Gym Leaders) will call you for a rematch, their Pokemon improving each time
- You will find opportunities to do double battles againsts two other trainers at the same time.
- You can also do 2v2 battles with computer partner against two other trainers.
- You can catch Ditto in the Desert Underpass.
- If a female or Ditto is holding an Everstone and you breed it, there is a 50% chance its nature will be passed on to the baby Pokemon.
- The path from Verdanturf through Mauville and to Route 118 has been straightened, which makes it a great path for breeding purposes.
- If you breed two Pikachu/Raichu and one is holding the Light Ball, the baby Pichu will know Volt Tackle.
- You are able to get both the Claw Fossil and Root Fossil instead of having to choose one.
- The Safari Zone has a new section that is full of Johto Pokemon.
- Once you fill the Hoenn PokeDex (not counting Jirachi and Deoxys), if you visit Prof. Birch he will allow you to pick one of the Johto starters.
- Move Tutors are scattered throughout the region.
- The Contest houses in Slateport, Vendarturf, and Fallarbor have been replaced with Battle Tents. These tents provide different skill games.
- All contests are now located in Lilycove.
- You can now choose either Latias or Latios.
- Rayquaza can be caught prior to the "elite" 4, although that is incredibly cheap.
- Both Kyogre and Groudon can be caught. Both are Lv70 (same as Rayquaza).
- You can catch Mew, Deoxys, Ho-oh, and Lugia, if the get the proper ticket from a Nintendo Event.
- Berries #21-26 now not only lower EVs by 10, but they also increase Happiness.
- The biggest addition is the Battle Frontier. It provides you seven different challenges that offers improved AI strategy (somewhat), including the ability to double battle either with or against a friend.
- More Johto Pokemon can be found in the Battle Frontier (i.e. Smeargle and Soodowoodo).
- Move Tutor moves can be purchased in the Battle Frontier.
- Vitamins can be purchased in the Battle Frontier for 1 Battle Point.
I am sure I am forgetting some things, but the above items alone make Emerald the best Pokemon game available.