Not sure why people are recommending ocean forest as it's generally too hot for plants 2-3 weeks and under.
Sunshine #4 or Promix HP both good for seedlings both similar product/source peat+perlite+micos. Great moisture retention same material as jiffy (peat) also what majority of ocean forest is minus amendments that will burn seedlings. Use whichever is cheaper in your region.
Light warrior works but is pricey from my memory.
Starting in Coco works, also coco+perlite go with whatever is cheapest.
Rockwool works as well as Rapid rooter peat based plugs
There's a newer mix I've seen at grow store called Kings Mix by some Humboldt company I was told it's peat+coco+light amendments/Bennie's and also works well for seedlings. I saw that this mix was cheaper than light warrior for similar product. Only thing was it came in a 3.0cu ft. Bag unlike light Warrior which I believe comes in as small as 1cu ft.
I think the Kings Mix ends up being cheaper per cubic foot than light warrior. Similar thing goes for Promix HP and Sunshine #4 they are I want to say 4.0 cu ft. and cost a bit but are a good value for the size. I think you can find sunshine #4 in a 2.0cu ft bag at some home depot's. Hope this helps