All three words are nearly equivalent, although outlook to me implies an attitude toward future events rather than a current state of mind. "From my perspective, the future looks grim, so I have a negative outlook. The viewpoint of my friend is quite different, so she is looking forward to next week." I think the exact phrasing would depend on the type of comparison.
I find the Wordnik relate pages helpful when I'm looking for the right word. I particularly like the "Same Context" section because it has words that are related and not necessarily exact synonyms of the word I searched for. Some alternate words that might fit your meaning better: insight, understanding, analysis, interpretation, conclusion, or treatment.
For example, "Dr. Z's analysis of the problem was thorough, but our insight into the nature of the relationships among the factors leads us to draw a different conclusion. Our interpretation of the significance of outliers is quite different."