Anon I use an M30 (pic related) and for a lot of games, 4 buttons is the superior choice. It's angled right so you can use your thumb to press 2 buttons at once (A and X or B and Y). There is no good way to do this on these 6 button controllers because if the buttons were angled properly, these controllers would have to be unnecessarily "taller". It's even awkward to position the thumb horizontally so you can press a row of buttons. At some point I used to bind B/Y and C/Z so that those were the normal 4 face buttons, but that's not a good solution either. At least the good thing about this gamepad is the fact it has a decent d-pad and 4 shoulder buttons (so you can use what would be equivalent to R3 and L3).
The only place where I'd say makes a lot of sense to have 6 or more face buttons is an arcade stick.