I like to swim the most. I go to the rec centre and lift weights some days and on others I'll swim some laps in the pool, then hit the hot tub. I've started up more regularly recently. It's so key, while tapering down to kick, I get a real mental boost from exercising. Sometimes after a long day of work after a good hard workout, sitting in the hot tub I get such a peaceful and content feeling, better than drugs I think, to be just normal as you are and feel great. I've had knee problems before too and I find swimming especially good because it's easier on your joints.