I love trying new fixed width fonts, but I keep returning to Bitstream Vera Sans Mono because it seems the sharpest at a variety of sizes (to my eyes, at least).
You read my mind - Bitstream is my goto font as is great cross platform too. Monaco has a bit more personality, but for some reason the font breaks down at different sizes and on linux or windows.
I'm going to try out fira as well - looked the best of this bunch.
However, I'm going to give Fira another chance.