I find the regular 3DS to be the perfect size to fit in your pocket, so for portability it's ideal. I also don't really have any qualms with the screen size, though the 3DS XL from what I've played is pretty nice, just not as portable.
In terms of the New 3DS, the regular version will have a bigger screen than the original 3DS so that's a plus, it also has the
lovely faceplates which I'm very excited about, some of them look great, and the SNES coloured buttons. For me it's a no brainer, the New 3DS' aesthetic and improvements are better than the New 3DS XL's which is just very bland in comparison.
Also the regular New 3DS is the focus in this adorable advert starring Kyary Pamyu Pamyu, when will your fave?