There are peat pellets, coir pellets, coir blocks and all the mixes bagged and homemade. Everyone finds a comfort zone.
I use peat pellets in the small (10-12 per) tray. As I have many varieties starting in a micro area, and with small trays can move each as needed. I tried the coir pellets, and was thinking something was wrong with me. Then realized the medium! I even tried half/half in one tray and that did it. The seeds in coir may sprout, but just didn't 'do'. For itty bitty seeds try to water from bottom, others much more casual. I remind myself that if these were outside would get watered by the great watering can in the sky.
Some are using the coir bricks. I could be way off, has happened before, but isn't that just compressed coir that you water to expand?
On a side note, I have plenty of pellets left when seeds just didn't do. I toss those in a container. On a pretty warm day I sit down with g-son (5) and we pop the coir/peat out of netting, and throw in a tub. This season I'll figure to add to any growing mixes I am using in the containers.
This just for discussion and perhaps what works for you.