My normal advice is the advantage of one over the other is dwarfed by the advantage of whichever you're skilled in. In your case that's not so helpful. :-) So I

My normal advice is the advantage of one over the other is dwarfed by the advantage of whichever you're skilled in. In your case that's not so helpful. :-) So I think Rails is (moderately) better for web development and Python is (much) better for stats/machine learning. But your choice will not make or break your project. It almost doesn't matter, so go with whatever language fits your taste. It's much more important to design a valuable product and figure out how you're going to sell it.