Hi, both are naturally occurring substances, vermiculite is hydrated magnesium aluminium silicate, while perlite is siliceous volcanic glass, both allow air into the compost, both retain isture, both are ph neutral, and neither break down in use, so once it's in the compost, it stays there, so in effect there's very little between them as far as garden use is concerned, Derek.

Use a seed compost, sieved, if you are going to prick out the seedlings and then pot on. Cover with fine grade vermiculite after sowing if you want.

If you are growing in cells and not pricking out, use a good multipurpose compost,sieved, mixed with either vermiculite or perlite, 3:1.

My methods and composts are here

http://growingforshowing.blogspot.co.uk/p/composts.html

I only use Perlite. Vermiculite can make soil too damp. Perlite add air to the soil and you get a lot less dampening off. I also use Perlite to add drainage for plants like Agave etc.

I'd go with Bamboo on this - vermiculite tends towards improving water retention while perlite is better to improve drainage.