It has to be F-15. had we gone for F-15 in the 70's we might actually have had some form of plausable AD capability for the last 2 decades of the Cold War.
imagine that...
We had THE best AD aircraft in Europe from 69 to 81 in the shape of the F4 (with the advent of the F15A). Look down-shoot down capability when even the US only had a pulse equipped fighter. Had we gone for a US platform to replace the F4 we'd have stayed up there but the F3, bless it, wasn't the right platform.
For me, HMS in the Tornado F3, a Buccaneer with decent avionics or a Lightning with 4 missiles. All would have been totally different jets.