I used to have one of the original GBA's but lack of a back light was just annoying, i ended up selling it after not using it much then I managed to bag a GB Micro off egay very cheaply and I have to say, the screen on the Micro is so much nicer to use.
It is a bit smaller but its fully back lit and very vibrant, plus the size of the Micro is nice. I find it fits in my hands pretty well