What is your favorite formula for starting tomatoes in the greenhouse?

My favorite formula for starting seedlings: do you mean fertilizer formula or growing medium? The growing medium can be one of several that work fine. Between 65 and 75% sawdust, peat moss, perlite, or combination thereof, and 25 to 35% sand makes a good mix. For fertilizer, we always use the Weekly Feed mix in a dilute solution, as described in the books.