Ruby & Sapphire feature updated graphics with weather effects, amazing sound, more than 200 Pokémon with over 100 new species, Double battles, and all set in the Hoenn Region. Emerald, an advanced version of the two, has a storyline based on Rayquaza, Groudon, Kyogre, Teams Aqua & Magma. The quest also has a Battle Frontier, where you'll need every bit of your strategy knowledge and cunning to win
I know more people who like RUBY over SAPPHIRE, but I myself think SAPPHIRE's got better version-exclusives, kyogre, ludicolo are better than their counterparts, however mawile and zangoose score over sableye and seviper. I myself prefer SAPPHIRE anyway, since I never use mawile/zangoose ^_^
When you are born, the world rejoices while you cry.So, in your life, do such things that when you are dead, the world cries for you while you rejoice.
I think you should play both at same time and also you can trade Pokemon from Sapphire to Ruby and vice-versa. You should try both of them and judge the games your self, because everyone has their own views.