i think there would be both. First off i think it would be more of a wal-mart vs. mom n pop type thing though. You know, the guy down the street who grows his own, is super dank, but doesnt have much selection/weight, or you could go to wally world where you can get almost any variety, in preset amounts that wont let you get smaller amounts, but they have almost everything, though you have to look real hard to find the super danks. And some curing required, kinda like assembly required furniture.

As for taxing it, it would be pretty tough to enforce, if you grew your own, its easier to grow your own weed than it is for tobacco or distilling or brewing alcohol. And if you ever get seeds, which is very easy with MJ then you can automatically start to grow your own and even copy their strains. Though large corporations would probably have a "strain" of their own, and all would be seedless, making the price worth the effort, and harder to steal a strain from competitors. But i think that if the government wants they could install a kind of grow permit which you would have to have in order to grow, and it says up to how many plants you can grow, which is decided upon based on how much you pay, for each plant will have a small "tax" charged for growing it, maybe 5-20 bucks each. Then if you dont have a permit then you can face drug charges similar to what we have now, whereas if you have the permit then you are in the free and clear. In fact that would give them a reason to spend most of their time focusing on MJ instead of the other drugs of choice by many peoples.