I have both.
The backlit SP does in fact have more vibrant colors. Especially the purples are really beautiful. But the Micro screen is in no way bad. Both the SP and Micro have brighter screens than the DSL or 3DS.
The Micro is really really really tiny. And that's not a bad thing. You won't even notice it's in your pocket. But if you're old or your eyesight isn't good, it may be straining. That said, it's certainly not too small to play.
The Micro, I feel is more comfortable. It's not itself hugely comfortable, but the SP isn't very comfortable at all.
You can get around the GB/GBC incompatibility on the Micro with an EZ Flash 4, which you should get anyway whether you go with the SP or the Micro. Playing the Zelda Oracles on the Micro is pretty cool actually.
My recommendation? Get both! I don't regret getting either one!