comfrey for apple guild

Hey folks,

I just finished measuring everything out, did my base drawing and am starting to design my apple and pear guilds, they have about 12.5' radius beds that just touch and overlap barely in one spot.  I decided to start on my food forest design with these guilds as the trees are suffering and I want to build a foundation in our back yard from there and move out

With that said, I am looking at using comfrey in the guilds, and was doing some research and came across this information: http://davesgarden.com/guides/pf/search.php?q=comfrey&Search=Search+PlantFiles

I didn't realize there were so many options, and was wondering if anyone has specific types for use in South East Michigan.

I am grateful for any help, and thanks.

I have been reading the site too: https://permies.com/permaculture-forums/1174_0/permaculture/the-value-of-comfrey

And others, just not sure if there is a really good option, or if they all just rock the world hard

Right now i'm leaning towards Bocking 14 Cultivar: http://www.horizonherbs.com/product.asp?specific=1606

Seems like a good choice for a suburban back yard food forest.