Anyone ever consider the MT83 Scorpion Pro for the front. It's DOT and every thing I ever read about it was good. I have one but have not mounted it yet.
I have run the 606 and the MT21 rears. I feel the MT21 is a hair better than the 606 off road but not a huge difference until you get in the sand or really loose gravel then I definitely prefer the MT21. The 606 wears noticeably better although the MT21 is not real bad in the wear department.
I've run the '83 front, and it didn't suit my riding style.
Its low-profile, and rewards an aggressive riding style, but tends to wash when you're going mellow.
The MT18 HD is DOT, looks much like the '83 except its higher profile and the side knobs aren't diagonal.
The '83 has a more open pattern, as well.
Both work really well, overall. The '18 holds a slight street edge, I think.