I think I'd probably have them both in mine.
HH is too injured to be considered for these lists right now. The potential is there but there is nothing else beyond that to rely on.
McKenna does have a case because he has performed well in AFL. He was awful in AA but he is a little younger than I thought, so that helps.
In no particular order:
Hall, Mountcastle, Hays,Rodriguez, Diaz, Tate, Ortiz, Kremer and Akin.
Those 9 are the ones I think you have to have in above those 2. I think I have Encarnacion as the 10th guy. His upside is really high but the K/BB ratios are terrible. Still, he has that potential that few guys in the organization have.
I would also put Lowther and Blaine Knight ahead of McKenna. I would consider Knight over Ortiz and Tate as well.
So, somewhere in the 13-15 range is the highest I can see McKenna and HH.