The Atari 2600 had pretty good vertical resolution (assuming you could set up the next line in 76 cycles) but limited horizontal resolution. A 3x5 font is possible, but good luck distinguishing N from M.

This font seems to use characters up to 5 pixels wide, which helps with its near-legibility.

The thing to do with a 3x5 font is to make the capital N into a giant lowercase n. Then M H and W all become similar letters, just with a different location for the horizontal bar.