Optically, they are pretty close in performance. My experience was that the HP was especially good at the long end. Mechanically, they are very different animals and this is a big difference. While more compact, the HP is mechanically less robust than the Cooke. The sections comprising its housing can become loose and rattly with even modest use. It is also a transitional design - not a true internal focus unit. Its front may not rotate, but it does track in and out. Its focus movement is very susceptible to entry of dust and mechanical wear. Angenieux corrected this in the HR.
The Mk-II Cooke is a true "fixed volume" internal focus design, but it has one unique quirk. Its zoom group tracks in a spiral cam, and therefore rotates during zooming. Some units have a noticable rotary tracking error as a result. This is very hard to correct, but usually minor in nature. Personally, knowing how sharp and robust these lenses were in rental service, I think they are the best value in a used 35mm 10-1 bar none. It is also far less bulky than the original Mk-I Cine Varotal 10-1.
Charles www.seriousgear.com