I've had my best results with pro-mix in solo cups, the mycorrhizae is already added.
When I transplant I will sprinkle a little into the hole. Don't remember what brand , what ever was cheap on Amazon.
I did not have much luck with the plugs. I tried germinating in them with a 20% success rate.I think the plugs are too dense, the seedlings do better with a looser medium, I.e. a rich loamy potting soil with added mycorrhizae.
For germination, Float Tech. Put your seeds in water ph'd to the proper value. They should float on top. Don't dunk them! after a couple of days of floating on top a tap root should sprout. Now you can plant them in your solo cups. This is the best way I have tried, better than the paper towel method.