Its one thing to say who you rather would have at this point, but a diffrent story be so convinced which of them will be better down the line.
Staal aren't a rushing D, he aren't a nr 1 PP quater back. Though he makes a really good first pass, and got tremendous poise playing hockey.
I saw his first preseason game in the NHL two years ago, and while he were in deep over his head in terms of strength ect, he passed and moved the puck extremely well. Actually created allot of offense, along with making some great defensive plays.
I defenitly belives Staal can become a very good nr 1 in this league. He got great raw tools offensivly, and is just so smart and poised overall. He is also 6'4.
Jack Johnson on the other hand is almost a finnished product. He'll just need to adopt to the NHL and he will be ready to go. He got a tremendous skill package.
But in the end, as we all know, playing D is so extremely much more then just pure raw skills. The most important aspect is to be able to play at a high level shift after shift, game after game, season after season. The one who can do that best in the NHL of the two will have the most success.