[DEVILsSON]

dude you have to break free of this 'what's better' mentality. It depends. It always fucking depends.

swimming is the lowest impact form of cardio just about so it's easier on the joints. You also burn more calories.

biking is probably second easiest on the joints and may potentially be more enjoyable for you because you can get to go mountain biking.

running is fairly hard on the joints but your body still needs some stress on the joints for adaptation....also you'll probably be able to produce better strength gains from hill sprints than from swimming...

then again all of this stuff is not really for 'strength' it's essentially conditioning based training.

Bottom line: DO IT ALL...variety is the key...