Anon

As a total force package with all that they can bring to bear rated for effectivness(IMO, of course):

Light Forces:

1) US Airborne Rangers
2) UK Gurkha
3) UK Royal Marine Commando
4) US Army 101st Airborne
5) US Army light infantry

Heavy Forces:

1) Any US Army heavy mechanized division
2) USMC Infantry
3) UK Mech Infantry
4) Israeli Mech Infantry
5) German Mech Infantry

Overall title:

Any US Army mechanized infantry division(by far)