Ignore the original GBA in favour of the SP if you can find a Model ASG-101 as opposed to the original SP model ASG-001. The backlit screen makes all the difference in the world, believe me, and the original GBA was uncomfortable to hold for long periods of time. Even better would be to just get a DS, as it plays GBA games perfectly as well as DS titles, and it'll only run you a bit more money.
*huggles*
Areala