I don't know that Mike Trout is the best player in baseball. Nobody knows that. Rather, based on all available evidence, Mike Trout is most likely to be the best player in baseball. Even non-Trout MVP voters concede that Trout is great while saying it's not just a best-player award. Insiders say Trout is the best. Outsiders say Trout is the best. He's young and he does everything, and it's all there in the numbers.
The most useful number for this is Wins Above Replacement, or WAR. It's the catchall statistic, and in 2012 -- Trout's first full season -- he was the WAR league leader, in both FanGraphs-brand WAR (fWAR) and Baseball-Reference.com's version. He was the fWAR league leader again in 2013, and then again in 2014, and then again in 2016. He didn't lead the league in 2015 -- he finished in second. Over the past decade, there have been seven player-seasons in which a player was worth at least 9.0 fWAR. Trout has been responsible for four of them. His average fWAR since becoming a regular is 9.4.
This time of year, baseball is all about identifying favorites and their strongest challengers. The Cubs are the favorite in the National League, and the Dodgers look like a strong challenger. Trout is the favorite to be baseball's best player again, and he's the favorite to post the best WAR. But which players might have the best chance to surpass him? He has, after all, been surpassed once.
Let's say Trout has another Mike Trout season and he doesn't get hurt. Who could be able to have a better season still?