I have to throw my two cents into this one....
You may want to search the forums as I just had a really nice thread about this same thing a couple of weeks ago.
After a lot of research & reading many threads on this topic, I decided to put pea gravel and sand in my run. I would NEVER do that again. 2 things happened--within just a couple of days, my chickens starting scratching the rocks up through the sand basically killing any thoughts I had of using my little pooper scooper to get any of the poo out. When I tried to use it, I got a little poo & a lot of small rocks that wouldn't sift out. You get my point. Also, my sand was a beautiful clean sandy brown color & it quickly turned gray like mud/dirt. So asthetically, I don't think it looks any better than the regular old dirt.
My plan is to start over again & dig out the rocks and put in just sand. I have found that the sand drains well, without the use of the pea gravel, though I do have a covered run. I'm also going to use more of a construction grade sand & not play sand.
The pros:
Its very easy to care for--the poo simply disappears. I rake it every other day or so for feathers, etc.
The cons: its UGLY!
To me, it does not look clean...The pea gravel is the major cause of that, IMO.
Overall, I think you will like the sand, especially if you have a problem with mud. Sand will definitely fix that. Just don't be surprised if, several months after you put it down, its not as asthetically pleasing as you would like.
Good luck!