I like Astrid better because it's not that uncommon, but like tararyaz said, Astrid could be made fun of once kids find out the other word for bottom. Kids might make fun of Ebba just because it does sound like you're saying 'Emma' with a cold. I don't think it would be completely hurtful teasing with Ebba, but she might get annoyed if people keep pronouncing her name wrong.
Oh, I love Alma best of all.
I love Ebba. I pronounce it - 'eb-bah'. It has great meaning for me, and I love it when people use it. In fact I've been thinking of adding it on my favorite list for the past weeks.
Astrid is great. I do have a younger cousin, Astrid. She's lovely, so I have positive images with it, along with Astrid Lindgren.
Alma and Agnes are sweet names as well, especially Alma.
But my vote goes for Ebba.
I think it was on The Office where they made a joke about Astrid sounding like @$$-turd? Anyways, that's unfortunate, because I do really like the name. But for a certain population here in the US, that will be the first thing they think of. As an adult with an appreciation for pretty names, I'm a big fan of Astrid, but I'm not certain a bunch of 3rd-graders will feel the same way. I've heard, however, that name-bullying has gone down a bit (in favor of other kinds of bullying, I'm sure), as there is such a wide variety of names these days--at least in the US.