DS Lite plays GBA games, so pick that one up. DSi is not worth the investment if you still wish to play the good GBA games. Have you played Golden Sun? GBA is awesome for that alone. 
For DS, seeing as how you are a JRPG fan (I think) there is plenty you can go with.
We have (some I have played)
Magical Starsign
Final Fantasy IV
The World End With You
Rhapsody
Chrono Trigger
Luminous Arc
Luminous Arc 2
Valkyrie Profile
Just a short list where some may seem kiddy but are actually quite good. You will find many old JRPG's but if you have yet to play them that is a BIG plus.
Stick with the DSL, the back catalogue makes it the better choice over the DSi. Do you really need a camera? 
iPhone = Great gaming device. Don't agree? Who cares, because you're wrong.
Currently playing:
Final Fantasy VI (iOS), Final Fantasy: Record Keeper (iOS) & Dragon Quest V (iOS)
