the new one XL or non will be 10x better than getting a used or new old one.
and i mean the new 3ds. it has better 3d (where its actually worth turning on. before you had to hold it weird to make it worth it) faster hardware and a second joystick.(kinda)
i've been debating selling my 3ds and getting the new model.. then i looked at my perfect nintendo collection and how up untill the wiiU i have literally every sku... decided to keep it and just save up
The 3ds is for a few games. you get mario kart, kid icarus uprising, super mario 3d land, pokemon, that kinda stuff. its generally best to get the rest of your games from the nintendo Eshop too. cause those are a good weekend of free time fun for like 7$.
be sure to grab a good SD card too. 8 gig or more