Myself, I prefer the fine stuff for most seeding, but I agree with Jonna that it really doesn't matter that much. I think it makes me feel better because there is more surface area of the seed in contact with the actual media, and I don't have to rely so heavily on high humidity to get the seed to imbibe sufficient water.
It's funny about vermiculite that the finer the grade, the less water it holds! Yet, that doesn't mean there is more air space in small grains; the opposite is true.
