During the times when I've been in the best shape of my life, it's always when I've been swimming. That said, swimming is boring as hell, and the view never changes, at least not in the pools where I swim.
I don't run, but I do walk about 5 miles several times per week, and love to be outside when the weather is nice.
This. Staring at that black line on the floor for half an hour is the absolute worst. When I had to train for lifeguard certification as a teenager the swimming was always dreadful but it no doubt gets you in fantastic shape.