More practically, create a habitable environment starting with well, Mars . Terraformers all seem to think Mars is their easiest handy target. They re probably right, but let us assume power in huge amounts becomes cheap enough to heat a world. Fusion might do that. Then reaching Mars becomes easy, because heat can become thrust for vehicles, but water becomes the bottleneck.
Tides keep Europa s deep water liquid.
Ganymede, though largely water, is probably solid. Good for mounting a mucking great rocket motor. With sufficiently powerful motors, this might become as easy as dropping a lesser mass in comets, and much faster. If we can t terraform Mars, all else is also beyond our ambitions. Don t worry about whether it s liquid.