Definitely, the term 'most valuable' is very subjective. What's valuable to one person may not be valuable to another. There was a Fangraphs article from Dave Cameron, whom I usually strongly agree with, which gave Trout the edge over Mookie because Trout made 386 outs as a batter as opposed to Mookie's 472 outs. The problem with that opinion, in MY opinion, was that he discounted Mookie's defense in his MVP bid. What???
I don't think there's a right or wrong here, because people's interpretations of 'most valuable' can be so different. Some people do think that most valuable means best.
If I had a vote, I think I'd go with Ortiz. I couldn't be upset, however, if Trout or Mookie won it.