As I mentioned in my post, it was strictly a gravitational consideration as Enceladus is much smaller than those and I thought it would be easier to get ice and water with the cost of time. Other commenters, however, have pointed out that although Enceladus' gravity is miniscule, it is deep in Saturn's gravity well which would be an extreme challenge to escape. Would that be a similar case with Europa and Jupiter? I guess Ceres would be the best choice then.