DSi = TFT - A slight edge above TN Panels (of that time*), better color quality, same response times, maybe only interesting as a side note: They draw a bit more power than TN panels and a bit less than IPS
Dsi XL = IPS - great viewing angles and color reproduction, albeit a bit slow, also take care buying used ones, especially from Japan, they tend to have a yellowing effect on the screen, the reason is, according to internet people, high humidity.
*My new 3ds XL TN panels looks great too after some color/gamma tweaking, people are hating too much on the technology, its response time is great for example and especially with a 3DS where you want to have your console in an angle to you so that 3D looks great you don't need the added viewing angle advantage of IPS. Fast paced games will have less blur, compared to IPS.
Modern Day IPS panels, as found in Computer Monitors, are very responsive these days, that's probably why TN panels get used less and less and will eventually die out. That said, my Odin2 Handheld has an IPS Display and sure enough, fast paced games have a blur, especially noticeable with 2D sprite-based games, emulating SNES for example.
