Best COIN platform

What kind of aircraft will be the best COIN platform ?

A helicopter
B single piston engined aircraft
C Multi piston engined aircraft
D subsonic jet aircraft

Please debate considering the kinds of weapons that can be deployed, loiter time , kinds of counter measures available for defence against AAA, SAMs etc , cost-effectiveness

For example lets take as an example of each class

A- Mi-24
b- T-28 trojan
C- Argentinaian Pucara
D- ALpha jet

or can use other examples please specify

Thanks