We built our agility field a year ago (120' x 120') and looked for the best Pacific NW outdoor option.
*Grass requires moving equipment before mowing, with fairly frequent mowing. Plus, it would be muddy for much of our Oregon winter.
*We looked at the rubber mulches but I read some things that made me worried about the health of my dogs, spending much time on it. Plus that was very expensive for the area we needed to cover.
*A friend used crushed granite (kind of like sand) which seems to be working OK for her agility field.
We ended up choosing cedar "hog fuel" (shredded cedar). We edged the agility field with railroad ties, leveled it, covered it with very heavy-duty landscape cloth and put about 4-6" of the hog fuel on it. It compacts down after 1 winter, kind of like felt, to 1" to 2" thick. The dogs can kick it up a bit, but it is easily raked back into place. It is moderately soft to run on, not as perfectly level as I would like, but really no worse than the dirt or sand mixtures in horse barns around here where we trial.
And the thing I really like is that it drains really well, and we can use it even in the middle of winter. And the dogs' feet aren't even muddy!
The main downsides are needing to rake it once in a while, and we added another batch this spring to fill in the thin spots. It is a bit of work to get it smoothed out. Weeds can grow in it, but with the landscape cloth underneath, they are very easy to pull out. Depending on the quality, it can have some larger wood chucks or sticks in it; we just picked those up.
When it is freshly spread, it will tend to stick to the dogs' fur a bit, but brushes out easily. After a winter, it doesn't do that much, as the hog fuel is matted down and no longer loose. It's not nearly as bad as the grass clippings in the lawn part of our field (as far as sticking to the dogs' fur!)
The dogs haven't had any problems with it being cedar (I know some dogs can be allergic to cedar).