Well I would personally buy DSi XL for sure. To me pokemon is one of those games that i play for a long time (i played 5 hours straight on my road trip) so the battery in dsi xl is huge for me. Also for some reason the screen sizes in the XL make me not want to hold a regular sized DS again. Plus there is likely going to be a 3DS xl and who know nintendo may release the XL sooner than they did for the DS since they found it to be popular.

SO personally DSI XL all the way. You may also find a good deal for one. I got a like new one a month ago for $90.

3DS all the way. The indepth 3d gaming experience Will make it that much more new and "GIDDY" Buy a extra batery. SOLVED

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$

unless i am missing something, The 3d doesn't work on pokemon......

3DS. The price is not that different (you can find a news 3DS for 200$), you don't get GBA retrocompatibility anyway, but on 3DS you'll have the virtual console (which could support GBA in the future); the battery is not a great problem, if you play offline it'll last even 7 hours yith 3D on. The obvious reason to buy a 3DS is because on 3DS you can play DS and 3DS games, while on DSi XL you cant. 3DS also has better multimedia, better online, better sound...IMHO the price is right, while the one of the XL is too high (but according to rumors it should get cut in a few days).

they will make one that does and he can enjoy what is new and coming.

Basically he can make sure he is ready for what is coming and play back catalog as well.

DSL if you want GBA backward compatibility for whatever reason.

DSi (XL) feel a lot more sturdy than the DSL.

If you're the somewhat clumsy type, go for DSi so you don't break it as fast.

Why would he need to be ready when he can just buy it at a later point. A new pokemon isn't coming for a real long time, and by then it will have gotten a price cut, and he would saved himself money.

Get the 3DS, it's backwards compatable with all DS games (guitar hero may be the exception, but I'm not sure).  The extra cost is worth it given all the fantastic games coming out for the system, which will surely include Pokemon gen VI in a couple of years.

And there is also the GB/GBC/SGG and hopefully soon GBA games one can download onto the 3DS

Those are the key words. By the time those games come out it will have gotten a price cut.