This was a great question brought up in the BA top 100 podcast. I think Harper's speed is his worst tool, and it's comparable to Trout's power and power is much more important than speed so Harper gets the edge there. Harper put up a 5.5 speed score. The major league average is 4.4. Harper per minorleaguecentral.com put up a 25% LD% in A ball. People are questioning his hit tool, but I would give it a 65 or a 70.
I would grade Trout like this
I would grade Harper like this
That adds up to the same OFP and both are above average in every category.