I think maybe Shawn might have been the beginning of the loss of credibility for the Federation Championship? But HBK sure looked good holding that belt though.
He sure did. My favorite HBK matches:
HBK vs Mankind (In your house "Mind Games" PPV)
HBK vs Undertaker (both Hell in the Cell "bad blood" PPV & WM 25)
HBK vs Bret Hart (any match these two had was amazing as they clicked so well in the ring despite their anomisity toward eachother)
HBK vs Kurt Angle (WM match)
HBk vs Vince McMahon (WM street fight match) HBK made Vince (a non-wrestler) look incredible in that match. A feet that is very hard to do.
HBK vs Hogan (Summerslam match) Made the aged hulkster look incredible.
HBK vs British Bulldog (In your house PPV)
HBK vs Razor Ramone (WM 10 ladder match)
HBK vs Diesel (In your House street fight match)
Thats all I can think of now although there are probably tons more.