Neither, get a ds lite. The DSI is just a waste because DSI games are mostly non existant and i am sure you don't need a camera or music player (if you do then ignore this lol). Too add, the Ds lite plays GBA games and that is huge in pokemon if you want to play the other important colors like emerald or leaf green. Plus, the DS lite has the best battery life i have ever witnessed. I am currently playing Platinum/Soul Silver because i just recently beat the old school pokemon on my DS lite so my team is raring to go. All this, plus its cheaper than the DSI.
Whatever you do though, do not go with the 3DS. It WILL get some sort of revision or price cut in the future and there are no games on it that are worth a purchase. I don't care how good pilot wings is there needs to be atleast 5 excellent games on a console to justify a purshace imo. You are basically paying 100$ more for 3D on a DSI with less battery life at this point and that doens't sound like a good deal to me.
EDIT: Oh, and you can get a DS lite on eBay for like 70$
