I went for footwork primarily, because you have to be able to maintain distance. Accuracy and speed are sufficient but not necessary conditions as regards out-fighting. I don't think defence is that important, since range control and getting to the punch first are often enough to neutralise your opponent's offence. A recent example is Martinez - in the traditional sense, his defence is abominable, but he makes up for it with movement, footwork (controlling distance) and speed (getting off first).
1. Footwork - The key to keeping the fight at range. Well balanced footwork to allow two things: A tall fighter to keep it at rnage or a shorter fighter to spring into rnage with long shots. The feet are the key in maintaining distance. By moving back and stepping into shots. Look at Alexis Arguello vs Bobby Chacon - the way Arguello always stays in a position to punch at long range, (not a good example just what I watched last) and to keep his prefer distance. Or Manny Pacquiao vs David Diaz - The way he kept the fight at long rnage with dynamic changes of direction then launched in with long straight punches then lept back out again. 2. Accuracy - To be a sucessful out fighter you need to be hitting the target to keep it at range. If you are missing you are allowing your opponent to get forward but also you are not doing effective work. The tall out fighter uses this to stop his man coming forward and when his opponent does go forward he can accuratly punch him to punish him for coming into range. Think Arguello vs Chacon again. The shorter outside fighter needs it as as he is launching himself in if he is missing he is wide open. 3. Speed/reach - These two are equal. Speed is good for getting of first to controll the nature of the fight. And reach is good meaning you can fight even further away. Will explain further in abit