Well simply put, as of right now, Mike Trout. He has had now three MVP seasons, has a higher WAR, and has better defense. If Harper can keep up his previous MVP season I would love to see how this argument turns out in 5-10 years.
Interesting topic. I personally think Harper will overtake Trout in the next year or two, and it was pretty damn close last year. Harper is also a few years younger than Trout.
Love Mike Trout, I mean LOVE the guy......but Harper is the better player. Harper is only 23 and his HR/AB and OBP is sky-rocketing. Last season goes down as one of the greatest ever for a player under the age of 25. Up until last season, I would have said "Trout now, Harper later" but now, I think it's all Harper.
I mean he won 88 games (lost 92) and put together a 19.5 WAR over 12 years in the majors (that's 1.635 WAR per year -- way more than Harper's 0.93 in his ten-year career, where he posted a mediocre 57-76 record).
It's Mike Trout. He can do it all including leadoff or hit cleanup. He can be a beast in the field or the basepaths. He's also got a much more proven track record.