That's why I like the far right click on the G600, uses my ring finger that usually does nothing and doesn't alter the grip, but it's extremely rare to have the three click system, it's usually just right and left click. For my thumb buttons I set inventory, map, and communications. While not perfect on other mice "look" on a mouse, especially if it's the only binding set to the side buttons, is better than nothing, especially if you don't want to get any additional hardware. Just an alternative I haven't seen brought up yet. Using side buttons regularly on a standard style mouse (like a G5/MX500) will change your grip and most likely throw you off. If I used a side button for look I'd find it cumbersome as well.
Head tracking is a great option because it uses movements and a part of your body that usually isn't used so it removes clutter and redundancy, but that's also why I like the G600's additional click. Head tracking will also work better for aircraft when you're using a joystick. Whatever works for you, there's no single best option.
