Personally, I don't care for the DSi simply because I don't like the idea of them coming out with a firmware update and possibly stopping your ability to use a flashcart. Sure, you can say, "Just don't update", but then you are locked out of the DSiware store, which makes it no more useful than the DSlite at that point...actually worse, considering no GBA support (phooey on iPlayer, that's just another accessory I'd have to buy). If I had a DSi, I'd want to be able to use ALL of it's features the way I want. As it currently stands, if you are just using it with a flashcart and not buying into any of the DSi specific fluff, it is then pointless to have anything other than a DSlite, since you really won't get much more benefit out of a DSi, other than DSiWare, which I can live without. DSi mode has yet to be unlocked via a flashcart.
And while I understand some of you not caring about GBA, I do. I have a veritable "pocket arcade" with my DSlite between all the DS and GBA games and homebrew I have instantly at my fingertips. With a DSi, I'd lose about half my library of games just in GBA stuff alone. I can't tolerate that. And I don't want to hear about iPlayer. I don't need it with my DSlite.
Plus, I can dump games thanks to the slot2, DSi has to use slow-ass WiFi dumping. As it is right now, I NEVER have to buy anything ever again for my DSlite. I have my CycloDS and M3 Perfect. I'm set. Why purposely go out and spend more money on something I essentially already have and have to spend yet more money on more new accessories to get CLOSE to where I was with my DSlite?
Of course, I'm also speaking from the depths of a software pirate's soul, so....
I vote DSlite. It suits ME. What suits you is none of my concern. You asked.