I used to use the spray paint method, and more recently tried brush-on latex.
I found the spray paint method easier, I just followed whatever directions were on the can, gave several light coats until light wouldn't show through. -and mask the sides, covered the top with a sheet of newspaper taped down to prevent overspray contamination, etc.
The brush-on latex is a better choice if you don't have a backyard or a garage or something, and need to work in your living quarters. It took me several coats, and I recently noticed a bubble where the heater cord stuck to the paint and pulled it away.
I'll touch up that spot one of these nights, so it shouldn't be a big deal, and it doesn't show too bad. I'll probably attach something to the top trim to keep cords from contacting the back of the tank as well. I used one of those sample-sized latex paint bottles in Home Depot, and got it tinted to black.
I think a painted back looks far superior to most of the other types, since it's uniform, and right on the glass, so you don't get gaps/dust/bubbles (with the exception of my heater cord issue...). And the black helps hide equipment/cords within the tank - they just blend into shadow, and make your plants/fish/hardscape the focus.