So, why Neustrom over McKenna? And why Grenier over Stewart?
While I like McKenna a lot, I'm holding judgement until we see more of what he does at Bowie over the coming months before determining exactly where he ends up. He fell just short of my top-15, but that might change by September.
As for Grenier, I feel that his defense will at least make him a role player that gets late-inning work and part-time at-bats. Stewart is more difficult to determine, because what is his role if his power doesn't translate to the majors? To put it another way, he's more difficult to evaluate than say Cedric Mullins, whose speed and defense will carry him if his bat doesn't cut in the majors. Stewart doesn't necessarily have that skill set to fall back on, so the power determines a wide gap between his ceiling (left fielder with average or above-average power) and floor (fourth or fifth outfielder).
I chose Knight over Lowther, because I think Knight's ceiling is higher. Yes, Lowther has more pro experience and success this season, but I like Knight's offerings better as a starter if he addresses his durability concerns. Even if the durability is an issue, Knight looks like a high-leverage reliever, whereas Lowther's bullpen role is a little more uncertain if he doesn't cut it as a major league starter.