I was a runner first, but years made my knee joints brittle, and biking is amazing to avoid pain there. And talking about knee joints, single leg squats are magic to restore them a bit. I was quite surprised.
I think about it regularly (cause swimming is one of the best kind of exercise I know of too) but it's less convenient logistically and also psychologically, you can't swim alone unless you have access to the sea or a clean calm river.
