I like the bigger screens of the XL devices and they do fit in my hands nicely, but the smaller ones are way more eye pleasing. Once a device that is intended for a pocket reaches a certain size it starts to look comical and all of the XLs suffer from that. They tend to look a little less like toys than their XL counterparts.
As for narrowing down the rest of the field, I think the DSi is out because the edges are a little too sharp and the camera looks ridiculous on the non-black models. The original 3DS is also out for me because of the oddly chamfered edges which the external cameras sit on, which breaks up the whole design. The New 3DS is close to the best, with nicely rounded edges and the heavier rounding on the (front?) corners is just the right amount. It's let down by the seam where it opens (not the hinge). It looks really silly since it's rounded over. The way the DS Lite closes and makes a continuous edge along the sides looks awesome. For that reason, the DS Lite is #1 to me.