Starting Outfielder 1:
Where to start, Trout is only one of the more exciting players in the game today and on the fast track to be one of the greatest players of this generation. He is an absolute monster (in a good way) in all categories. He's led the AL in Runs Scored the last two years, he will give you power, speed and batting average (and he also led the league in walks giving him a nice .432 OBP). And he doesn't even turn 22 until August. Since most players hit their peak in their last 20s its almost mind blowing how good Trout will likely be once he gets some more playing experience under his belt.
I know highlight reel catches aren't a fantasy baseball category but they add to the growing legend of Mike Trout. Even the one statistical weakness from 2013 (-0.9 dWAR) is a bigger indictment on the general state of evaluating defensive performance than anything wrong with his game.
There seem to be no real downsides to his game. It looks like Trout and his agent are working towards what will be a likely lucrative extension that may distract him from only being uber-awesome instead of uber-ultra awesome. Also, he's starting doing commercials such as Subway so maybe in like 15 years he'll be in the Peyton Manning zone where people are all like is he just that dude from all those commercials. Since, i'm going to hypotheticals on the Cons side, there appears to be no downside.
His most similar player through age 21 is hall of famer Frank Robinson. He had a very strong age 21 season .322/.376/.529 29 HRs and had several more great seasons. Out of his most similar batters through age 21, seven of them are in the hall of fame. Bottom line is that Mike Trout seems to be on the fast track to Cooperstown and anyone with him on their fantasy team already has an advantage over their competition.