If the choice is between Gunnison Reservoir and Nine Mile, go to Nine Mile. There used to be a few bass in Gunnison, but it was drained three or four years ago and about the only thing there now are carp — the DWR doesn't waste its time planting it. It's a murky reservoir because it's full of the water that drains the wetlands in the middle of the Sanpete Valley.
Nine Mile, on the other hand, actually has some pretty good catchable rainbows, as does Palisade. The canyons east of Mayfield (12 Mile) and Sterling (6 Mile) will likely be muddy this weekend (and full of hunters, if that's a consideration), but there are fish there in the ponds and creeks.
If you're not opposed to the canyons, there's also a small reservoir up Manti Canyon called Yearns that's sort of a local fishing hole (caught my very first fish out of there when I was five or six.)