Is it appropriate to 'build up' your findings in a paper?
Either way could be made to work, but consider:
If the proof methods of the three are essentially the same, then the first way would be boring (possibly).
But if the second builds on the first (etc) by using different insights and methodologies, then the first way might well be superior.
Don't just consider the progression of results but of the progression of proofs and, especially, insights, that get you to the final result.
And if the latter is the case, make sure you emphasize those insights. They might (and often do) lead to developing other ideas.