This is my Viking blood talking.
I prefer leeks to shallots. We Vikings consider shallots to be the leek of the weak. What made our conquering of so much land so easy was that we ate leeks while those we conquered ate only shallots.
That being said, I like a combination of mediums. Sand from the central, east coast of Norway, and volcanic ash sifted from tons of melting glacial ice from Iceland. It gets processed at a glacial ice melting plant in the Faro Islands. You can't buy it, of course, and can't find much information on it online. It has to be picked up in person and smuggled into Canada before the US. If you don't happen to be a Viking, you're out of luck anyway. If you have lost your family's Leek soil recipe, you're one suck Viking.
Keep us updated with pictures, whatever your choice.