This is the first thing I thought of. Trout is, literally, the best player I've seen play in the last 15 years probably. He's just great at everything. And I mean overall player. Some great hitters out there.
The first 2 years of Trout were the best first two years I've ever seen of an MLB player. But he's hacking a lot more now, hasn't been running quite as well on the bases, and his defense has fallen apart. Perhaps, hopefully, he's been playing through some temporary injury and he'll return to form at least defensively.
Going by UZR, Stanton was about 12 runs better than Trout defensively last year. Trout went from a +13 run fielder (very good, especially considering he only played in 139 games) to a -10 run fielder in 157 games this season. Unlike Stanton, Trout doesn't have a very strong or accurate arm and much of his defensive value depended on his speed and athleticism.
Trout's strikeout rate went from 21% in 2012 to 19% in 2013 to over 26% this year (Nearly as bad as Giancarlo's strikeout rate) with less power than Stanton.
All that said, I'm a huge Trout fan. But if we're going to see more of the 2014 version than what we're used to, he's no longer unquestionably the best player in baseball (despite what the MVP awards say...of which he was robbed of in 2012 and 2013). I'd still prefer Trout over Stanton, but Trout's speed and defensive regression and K rate are troubling. He's trending more towards a 1.5 tool guy (power and respectable speed for a player of said power) than the 4 tool phenom (never had an arm).