At the current moment.
I own both a regular GBA, and an SP.
I have friends who own a regular GBA, and i have friends that own SP's.
SP is *FAR* superior in almost every way, And it would be FOOLISH to buy a regular GBA after playing it. The battery alone makes it worth the extra money, because i know for a *FACT* that I've spent over 30$ on batteries for my GBA alone, and I'm not including a peripheral light.
The SP's fold out design not only makes it sexier and smaller, but it also prevents the screen from getting scratched, which has been a major issue among every GBA I've ever seen, my own GBA has some horrendous scratches, and a big dent on its screen. My SP, which i literally haven't left alone since i got it, Has yet to have any scratches or similar problems at all.
I never have to worry about stealing batteries from other sources (kitchen clock, emergency flashlight, Wavebird(and yes, that order >.>
anymore, because the recharger and how long the SP lasts take care of all of those problems.
Playing in the dark is cool.
I can actually listen to the game music now, i don't have to worry about it draining my battery life!
I love my SP, and its hard for me to go back, I'm keeping both for multiple reasons, however. SP is the way to go that 30$ is worth way more than the problems the first GBA had.