3DS:3DS Model Differences
Page content & researching collaboratively taken from io55.net's 3DS page with permission.
Models
Models are arranged chronologically.
Nintendo 3DS (2011-2014?)
The original version of the 3DS. Easily identified by it's smaller clamshell form factor, lack of a 2nd analogue stick, non-colored ABXY buttons, and slightly more “ridged” outer shell. With the later arrival of so many varying 3DS models, the original 3DS has somewhat lost it's position of relevance when compared to these later models. The only two things which may give the original 3DS an edge is that these systems have a superior port of Linux (at least, for right now), and that two particular games (Metal Gear Solid 3D, Resident Evil Revelations) may work better on a OG 3DS/3DS XL + Circle Pad over the “New” 3DS and it's built-in 2nd stick.
Nintendo 3DS XL (2012-2015?)
The original XL version of the 3DS. Easily identified by it's larger clamshell form factor, lack of a 2nd analogue stick, and the start/select/home buttons being obvious rectangles under the bottom screen. Outside of the larger form factor and minor button changes, the status of the original 3DS XL is essentially the same as the non-XL original 3DS, although the OG XL does have a slightly longer battery life.
Nintendo 2DS (2013-2017?)
Nintendo's first foray in removing the 3D. Very easily identified by it's “slate” form factor which does not close, plus the lack of a 3D slider. Outside of it's very odd form factor and lack of 3D, the 2DS also has removed the stereo speakers and downgraded from the screens found on the OG 3DS systems, bringing the 2DS sound output to only mono without headphones and it's screen quality to guaranteed-TN. Furthermore, battery life is somehow slightly longer, and sleep mode is instead activated by a switch. Lastly, the Circle Pad Pro will obviously not work on these systems, making these really only matter in the realm of budget, as the OG 2DS is easily the cheapest 3DS on the 2nd hand market.
"New" Nintendo 3DS XL (2014-2019)
Nintendo's first foray in making “Pro” refreshes of their systems. Oddly, in Japan, the XL released a few days before the non-XL “New” 3DS. Easily identified by it's larger form factor, colored ABXY buttons, presence of a 2nd analogue stick, camera located above the top screen, home button below the bottom screen, and presence of a 3D slider. Improvements coming with this model are very fully fledged, including a 2nd analogue stick, integrated NFC, faster CPU, more RAM, better 3D capabilities + head tracking, a small library of exclusive-to-“New” games, ZL and ZR buttons, automatic brightness adjustments, and more. These are essentially the strongest version of the 3DS when it comes to raw power and features, with their only downside being a somewhat higher price on the 2nd hand market.
"New" Nintendo 3DS (2014-2017)
Very similar to the XL version of the “New” 3DS. Can be identified by it's smaller form factor, 3D slider, and presence of a 2nd analogue stick. The only major differences between the XL and non-XL “New” 3DSes, is that the non-XL has interchangeable faceplates, plus it's a tiny bit larger (both in screens and form factor) than the OG non-XL 3DS systems. This makes the non-XL “New” essentially the same console as the XL "New", except it's smaller and more personable. Alas, the non-XL “New” does have one downside in that it is easily the most expensive of all the 3DS models out there, due to it's relative unpopularity in much of the world compared to the XLs.
"New" Nintendo 2DS XL (2017-2020)
Somewhat between the “New” 3DSes and the original 2DS in capabilities. Easily identified by the non-slate clamshell design, the camera being in between the two screens, the home button being to the bottom left of the bottom screen, the lack of a 3D slider, and slightly “rounded” top and bottom halves of the system. Most of the changes between the “New” 3DS and “New” 2DS are downgrades, as the “New” 2DS has poorer screen quality (guaranteed TN), less powerful speakers, and a slightly cheaper feel and function all around. Of course, with the “New” 2DS being a budget-oriented console, this comes as no surprise.
References
https://en.wikipedia.org/wiki/Nintendo_3DS
https://en.wikipedia.org/wiki/Nintendo_2DS
https://en.wikipedia.org/wiki/New_Nintendo_3DS
https://en.wikipedia.org/wiki/New_Nintendo_2DS_XL
https://www.destructoid.com/nintendo-has-seemingly-discontinued-the-original-3ds/