I keep Emperor Tetra with an Angel. They are quite large for Tetra,and have awesome colors. The Emperor's were a bit nippy when I first put them together,but I have no issues keeping them in the same tank now.
The tank is only 29gal so I think congos and silver dollars are much too big. I'm leaning towards lemons or pristellas. All depends on what I find at the LFS.
I think it depends on the individual Angels.