They all have flaws. If you're looking for objectively best, then that would be either of the N3DS models, just because of their higher processing power and compatibility with N3DS exclusives.
N3DS good if you like customizable faceplates and portability, N3DS XL good if you're into bigger screens. N2DS XL good if you really don't care about 3D because it costs less, but it's built very cheaply and it shows.
Hinges are an unnecessary point of failure, and I can't stand them. Therefore, 2DS wins by default. It's not without flaws though. Just like the N2DS XL, it's built cheaply, in various ways (lack of modularity is an issue but I won't really get into that here), but at least it feels rather robust in the hands and the plastic feels like it's decent quality. I'm really not a fan of the squishy rubber dome buttons though, I'd much rather have clicky buttons like the other models. And I guess the mono speaker might be a problem to a lot of people, I really don't care though.
I might like hinges more if they were built more like what the GBA SP has. That design is awesome. It feels super robust, there's so much more room for ribbon cable to breathe, and it's designed in a way that taking it apart and replacing the hinge (or the entire shell) is as frustration-free as possible. I can't trust Nintendo's hinge design ever since the DS Lite. I'd much rather go with the hinge-less design.
It's not even bad, anyway. It's less portable for sure, but considering that I never really take it out of the house, portability is not a concern. And if I
did want to bring it somewhere, I have a carry case for it, so the screens aren't really at risk of getting damaged, unless some spectacular accident happened.
It's somewhat nostalgic, too. Goes back to the GB/C days and such when handheld consoles of the time didn't have hinges. Really nice with VC titles. And the absurdly low price point for the console is a really good thing. This thing plays the majority of all GB, GBC, GBA, DS and 3DS games, plus NES if you are so inclined (and I'm not even including 3rd-party emulators), and it only costs like $50.
If I were to get a N2DS XL, this would probably be my preferred model, but it'll probably never be released outside of Korea and Japan, so hey. That being said N2DS XL has enough flaws, and I don't have enough of an interest in the N3DS-exclusives, that I probably will never bother getting one.