Ask Grant what he uses!
http://www.thehotpep...on/page__st__40
I am not a fan of some seed raising mixes, I think loose woody mixes aren't much good for germination. Germination mixes need to hold moisture not air, they need to take the seed cap off. Drainage and air to the roots isn't important if you transplant them soon after germination.
If you look at some big growers, they use jiffies, and keep them so moist they are mouldy.
Airy wood chippy mixes like amgrow aren't very good for germination, if the seeds dry out, they are done for sometimes.
You shouldn't be worried about root development and air getting to them, you should be worried about keeping them moist. A lot of people germinate in plastic (containers or zip lock bags) on a paper towel.
Debco seed raising mix is OK because it has some sand in it to hold moisture, but it is still a little to much wood chips, and if it gets dry it does go hard
I don't know what plantcare seed raising mix is like, but out of your three examples I'd go for the coco coir brick, which will hold moisture well kind of like a jiffy pellet.
A woody seed raising mix may make it too easy for the seed to have a an easy path through all the big airy gaps and have a stuck seed cap, or worse still, get stuck under a wood chip.
Then after germination, repot it into some decent mix so it can develop roots in a good airy mix. Coco coir holds moisture well without turning rock hard if it dries up a bit, like some potting mixes can.
edit: I've also read the the amgrow is mainly compost, with a little bit of peat, and very high in ferts