I have a few.
Our community has a lot of nice parks; I've been to all of them. Different parks have different features, and so I have different favorites for different things. For instance, Avery Park has nice fields, great picnic shelters, and a beautiful rose garden, but its playgrounds suck; they're incredibly unsafe, with one playground having the end of its slide about 3.5 feet off the ground, with no significant cushioned surface underneath. It's my favorite all-around park in this area, though, because despite the bad playgrounds, there is an awesome interactive sculpture for kids to play on, and a decommissioned steam engine that's been modified for safety for them to enjoy.
Willamette Park is another favorite. It has some really nice fields, a disc golf course, a great playground, and some enjoyable trails along the river. There are also places with bank access, where you can go stick your feet in the river. I never liked the blackberry canes that seem to be everywhere in this park before this last summer, but then I took some kids berrypicking there, and everyone had such a great time that I've changed my mind.
We've also got a variety of smaller parks inside the city. I live close to a few of these; the closest is a block and a half away. They're favorites of mine because we use them so frequently. When friends feel like tossing a disc around, we just head to the closest park.
As for state parks, I really enjoy the Samuel H. Boardman Scenic Corridor. It consists of a string of waysides on the southern Oregon coast.
Oregon State Parks and Recreation: Rates We were out there last week, and had a great time climbing Cape Ferrelo. My other favorite, also on the coast, is Hug Point.
Oregon State Parks and Recreation: Rates There is an old wagon road cut through the rock of one of the points at the park. It's one of my favorite places to visit.
My favorite national park would have to be Zion.
Zion National Park (U.S. National Park Service) We've talked about going back, and I'd like to. There are a lot of hikes at Zion I didn't get to do when I visited. It's so beautiful, and there are places there that are extraordinarily serene. It is one of my favorite places on Earth.