Wanted to weigh in here, having owned multiple *new* 3ds consoles, 2 limited edition XLs, the Majora's and the Metroid (first one with IPS and second with TN), and 1 regular size. They're just better constructed on the whole than the 2ds xls.
Not to say that the 2ds build quality is crap or anything. A lot of the difference in subject quality probably comes down to weight. They're simply a lot heavier and give the impression of more solid construction. I bet you could throw both the 2ds xl and 3ds models around a bunch and not have any problems though.
Adding to this feeling is speakers' placement in the bottom of the 2ds--at anything more than 1/4 volume, you can feel the system vibrating a bit. Not a big deal for headphone users but for the rest of us...that was what tilted me in favor of the more expensive models.
2ds is easier to hold for extender periods, and feels a little less 'bricklike' so you can be more agile with your inputs. TN panels are going in everything now, so it's very difficult to find even a New 3ds XL model with an IPS. The TN in my Metroid unit is very good though, not indistinguishable but more than tolerable. The 2ds's was a little less so. That may be down to luck of the draw though, as my sample size was far too small.
I'd say save the money and go 2ds if you use headphones half the time or more.