Is there a difference? Which is best?
Vermiculite is natural Mica based mineral material that is processed into various forms for various uses not only in gardening.
Perlite is a naturally occurring silica based rock that is mined and expanded to for what you see in the garden centres.
Both can be used to improve drainage/aeration in potting/seed compost and can be inter changeable in that way.
Vermiculite can be sourced in various grades from very fine to gravel size. The very fine can be used to cover seeds rather than compost or soil. This can increase germination rates and help reduce problems such as damping off.
I tend to use what ever is too had for drainage, but prefer perlite and I use fine vermiculite as a seed covering when planting tomatoes and some other small seeds.
HTH
Jerry
i use perlite to open up drainage in pots, and vermiculite for covering seeds when sown.