Perlite vs Vermiculite for Starting Mixes?

[Greatgardens]

I use and very much like Burpee's Coir Organic Seed Starting Mix, but I am mildly concerned that it does not have enough porosity. Incidently, overall I've had much better germination using this Burpee product than with peat starting mixes.

So I plan to make up some test batches with a perlite or vermiculite addition -- say 10% as a starting point. I realize they are slightly different in their effect, but I am leaning toward the vermiculite mostly because of its finer and more uniform particle size.

Any thoughts on one versus the other for this application?

-GG