TR.
Reasons:
Trust Busting.
Willing to negotiate with workers and unions.
Increased regulation of business in a time it was desperately needed.
First President I'm aware of to promote conservation.
Improved the quality of food sold by making it illegal to have misleading labels.
Good approach to foreign policy (speak softly and care a big stick).
Also, got the ball rolling on healthcare by being the first President to talk about it as an issue.
...Aside from the second one, and even that's questionable, every point on this list is misleading at best and propagandistic at worst.