Yes, you can tune an M4 or M16 equally. My MP5 is well tuned. Fielded yesterday outdoors and was making 100+ ft shots and getting kills without any issues. However, at the end of the day, my C7A2 (also well tuned) can easily reach out and touch someone 125-150 feet away, which is out of the effective range of my MP5. As The Saint said, it depends on your style of play. I consider myself a rifleman, and I prefer shooting people at long range - and staying out of their weapons' effective range. That's my style of play.
You can also have the best of both worlds if you can get an ICS rifle. With their split mechbox design, you can have multiple upper mechboxes with different springs and matching cylinders for different barrel lengths. You get one base gun, a couple of different upper receivers / front ends with different upper mechboxes. Want an outdoor gun for long range? Swap in a new upper mechbox with a 400 fps spring and full cylinder, and an M16 front end. Want CQB? Install an upper mechbox with a ported cylinder and a 350 fps spring along with a shorter railed M4 front end. And you can perform the full swap in a couple of minutes. That gives you one very versatile gun that will suit any gaming scenario.