I think I've flip flopped from a similar poll earlier in the year. This time I picked Coleman. RG3 looks better than expected. Even though it's preseason it's still better than looking horrible. Treadwell you would hope turns into Nuk. Coleman hopefully AB. Part of what makes AB great for FF is Ben and the Steelers offense so, I don't mean AB in terms of FF production. Basically, I'm saying if Treadwell and Coleman hopefully turn into the elite, I consider them a wash.
However, if you start to look for lower level comps and just look at pure physical traits, Coleman can fill more roles. He can be pure deep threat like Mike Wallace was, he can be shifty deep threat a la Desean Jackson, he could be a little bully like Steve Smith, he could be the sneaky slot like Welker or Edelman, he could be that secondary stud like Randall Cobb or Jon Brown. I don't know if the Brown/Cobb comp is an actual role like the other types I mentioned. If Treadwell doesn't turn into Nuk than how many other roles could he fill? A big slot like Colston. Or a big secondary option like Decker.
Route running + physical skills is what sets the elite apart. If both are great then who cares? You're punishment for picking the wrong elite guy, is a slightly lower elite guy. Darn. If Treadwell struggles with routes, really his only weapon will be to box out/"my ball" against defenders. Coleman could do this too (see Steve Smith). It would probably be easier for Treadwell but the point remains. Coleman, however, also has the ability to use speed to get open. Or use agility to beat coverage.
***Both are really close though. I answered with the mindset of I have to take one and can never trade them. Otherwise, it's easily Coleman because I think year one will be much better for him. I think Treadwell likely has a slower start to his career or at least in year one. Say 45/550/2 then explodes next year. Kind of like Allen Robinson. In theory I'd take Coleman now and Treadwell next year based on my projected/expected prices. But that has more to do with value than player vs player.*****