I want RPG with awesome story and lenghty gameplay and the nominates are Crimson Gem Saga, FF 2 (already have FF 1) and Chaos Rings.
First off, this belongs in the "Mass 'What should I get?' Thread" for future reference. And as for your question, it's definitely between Chaos Rings and Crimson Gem Saga. The real question is how much money do you have to spend, as well as would you rather have a more story-based, traditional RPG, or something a bit newer and less story based?
If the main thing is story, definitely Chaos Rings. It has a much deeper storyline than other appstore RPGs. However, CGS beats it on core gameplay.
Perfect example of why it is completely pointless to ask other people to make a choice for you, as opposed to making one yourself based on available impressions. Also I find this amusing.