I've never really grown canna in soil - I started in hydro (in June!) and had a nightmare with it, moved to coco and have never looked back.
I don't like soil because no matter how great your soil or soil mix is, it doesn't drain like coco does - so you can overwater. Coco can be watered multiple times a day if you want and not worry about it because coco retains only what it can, leaving air for the roots to breathe. Also, coco is inert....it's like using clay pebbles or cellmax....it's essentially a hydroponic medium that looks and acts a lot like soil, only better.
Roots LOVE coco....more roots = more bud. The only people I know who grow soil do so because they prefer the taste and/or grow organically. If this is you, soil is the one for organic goodness. If not, I can't see the benefit of soil over coco....or rather, any taste improvements aren't worth it compared to the myriad of other benefits. And my weed tastes awesome, and it's not organic....just make sure you flush well....
