I still say beunos aires tetras for the win, they are very fast for dithers, and are a tight schooling fish, I have 8 in my Dempsey tank.
I have a 135 gallon with an oscar 6", 4" convict, another 3" con, red devil 3.5", and some sort of vieja/paratheraps 3.5"...i put in 13 buenos aires about 2 months ago and figured i was good to go since my cichlids were so small...i'm down to 5...i assumed it was the oscar...NOPE...it was damn eclipse catfish (about 6-7") that i always forget about because i never see him. Caught him about a week ago with a HUGE stomach and i was missing another BA tetra...Silverdollars have the best chance imo. I still have 2 from the original 6 that i bought 8 years ago...i've considered trying rainbowfish since they get about 4" and have high bodies.