It's also worth noting that link play is hellish with the micro. It does not feature the usual GBA link slot and the necessary cords are only available from Nintendo. This means that if you want to use a flash cart, you'll need to get one that doesn't use the GBA's link slot. Most newer and higher end carts will be compatible, so that shouldn't be too much of an issue.
I recommend holding each one for a bit before you make your decision. I was near ready to fall and pick up the SP when they came out, but then went over to a friend's and tried his out. I HATED it.
I, like everyone else, gave the micro nothing but crap for years. When I tried it out though, I fell completely in love. In fact, after messing with mine, my three closest friends went out and got their own. All of us had the original GBA and two even had the SP. I recommend the Famicom/20th anniversary edition, by the way. It's gorgeous.