here's what i've been obsessing over for 2+ weeks now. K. kindly sold me their 2016 black friday "New" Nintendo 3DS (non-XL!) and i've been goin nuts updating its hax and curating a library (Nintendolife.com reviews are invaluable)
the state of 3DS custom firmware (CFW)? outstanding. obviously piracy is a huge selling point, but even if you abstain CFW has great benefits like running games at the New 3DS's 4x clockspeed, which took one game i'm playing from ~15fps to a solid 30. amazing. CFW is invaluable.
k͕̽/\̲̻͍ͬ̾̽tn͑̿͐ǰi̘͕̒̿å 
Nobody does 
It's a neat gimmick, but uh, I turned it off after a few days.
But the screen itself, and the build quality is really good. Some version of the XL also has a IPS display, which is super friggin' sharp, so looking out for those alone makes it so much better to play on it.
True...
@katnjia @noiob i've heard 2DS's build quality is less than premium. unsure how it fares in ergonomics, but wouldn't be surprised if it's comfier than the clamshells
but yeah, i think 2DS will only have TN screens
3DS XL units with IPS (either single, or both screens) aren't exactly common and command a premium on places like eBay. but damn, does it look better than TN!
can also pay a modder to replace an XL's screens with IPS. (replacing the top screen is so fraught/difficult DIY isn't recommended.)
I mean if you're going to DIY it, you'll have to find an IPS panel to a good price. The process of changing the screen isn't necessarily difficult per say, but it is very time consuming:
https://www.ifixit.com/Guide/Nintendo+3DS+XL+Upper+LCD+Display+Replacement/25070
You also have to work in a clean room, else you'll find yourself assembling the unit half way and there's like dust speckles on the glass you just noticed because the light was right, and you goo FFFFFFFFFFFFF 
@noiob @gatewave I'd go with the 3DS XL; the prize used for both consoles are almost the same.