I disagree on Wonderswan. The Crystal, being over $100 now, isn't a great option unless you have a lot of color games. If what you have most of is B&W games, they are worse on the Wonderswan Color and wasted on the Crystal. The B&W Wonderswan is very cheap, about $10 - $20. I'd say it's much better value than the Crystal if you like B&W Wonderswan games.
The Game Boy Color is nice, but I find the postage stamp-sized screen to be a letdown. I like that the Pocket has a bigger screen. The Super Game Boy 2 is tethered to a home console, unless maybe you have a portable SNES clone, but that's just ridiculous.
Also, the original GBA has a completely horrible screen, it's second only to the Wonderswan Color in darkness and unreflectiveness (actually, the WSC is a bit more reflective). The original SP is okay, sort of blue-ish though. The SP2 looks great until you ask it for motion, I find the response time to be annoyingly slow. It's just slow enough that if you play an original Game Boy (Color) game, the pixels will become misshapen.
Interesting. I've only owned a B&W swan and B&W games. Can somebody do a side by side comparison of a B&W game displayed on both the original B&W & Crystal consoles?
Also, how does motion blur fare from the B&W to the Crystal?