Here’s a picture which shows that Miracle Gro and Gravel tied as the the best medium for rooting plants. It’s hard to tell from the pictures, but Gravel had 5 flower buds and Miracle Gro had twenty. Gravel also was a bit bushier with larger leaves. Miracle Gro was definitely taller, but was less filled out and had smaller leaves. Gravel also had a lot more roots coming out the bottom. These are the same plants planted at the same time. Either one would do well for rooting cuttings.
From left to right you have:
Perlite – Fertilome w/o fertilizer – Charcoal – Gravel – Miracle Gro.