Which planet best to escape Earth when our sun gets too hot?

Not within our lifetime, but eventually our sun will expand to a red giant engulfing the orbit of earth. Assuming humans evolve technologically, which planet would be best for human migration? The outer planets seem to have more stable magnetic fields, and ice that would by then melt into water. Perhaps human genetic engineering would by then be capable of directed mutations for gills and equipment to survive in much different environment.

I imagine staging and resource acquisition on Mars. Then a quick shot around JupiSaturn to a nice thirteen moon surf on Neptune… or perhaps a Neptune moon would be new home?