Okay, I think my Pem's favorite activity (if you don't count sleeping as an activity) would be walking. Actually I like to call it "surveying her domain". I believe she thinks of our neighborhood as her kingdom and it's her duty to check on everyone and everything now and again to make sure it's all still in order.
For my Cardigan, his favorite activity is playing with other dogs. Everything else pales when a potential playmate is around. I've even seen him pull off sheep to go check out the Great Pyrenees on the other side of the fence. I can just imagine my dog thinking "you know that big guy MIGHT play with me..."
:D