I bought both a GBA and a GBA SP. The SP was FAR superior. It was seriously like night and day. I'd never want to go back to playing without a lit screen, or without a built-in rechargable battery, or without a shell to protect the screen. Even the clicky buttons were an improvement; they made it easier to pull off combos in Street Fighter. Only downside: no headphone jack.
I never bought a micro. Aside from the headphone jack I don't see what makes micro better than SP.
I currently do NOT own a DS. I was originally waiting for some more good games to come out. Now I am waiting both for more good games to come out and for the lite to be released in the US.
I'm not yet decided on what color I want. I'm leaning towards Navy. I'd like some input in this regard: on which color do you suppose fingerprints will be least visible? Because I've read that the DS lite has a new clear plastic coating which unfortunately exposes ugly fingerprints.