I visit Montana every summer in my TC to fish with my cousin from Dillon. Take a look at my blogs for the last few years for possible camp sites. If you click on "Campsite Map" at the top you can get a quick idea of where I've camped in MT. I've been all over the western half, including both the areas you mentioned.
As far as the Big Hole, there is a small BLM campground (East Bank) right on a nice section of the river. It's 8 mi W of Wise River. See my 8/28/08 blog entry.
Give the Beaverhead River a try in the Dillon area.
Feel free to email me via my website with any questions, or PM me here.
I'll be returning next summer. Maybe our paths will cross. :)
Have fun,