Ski-ing is the best. Sadly local availability of slopes and snow restricts me to doing it once a year. (ski-ing, that is)
Ski-ing is great downhill, but dull up.
Cycling is second. Uphill is hard work, but great at the top. Down is fun, particularly with added "weeeeee!!!"
Walking is third. Like cycling, going up hill is the pain to get the pleasure at the top. Unlike cycling, though, there is no pleasure in going down.