Just my 2 cents, but anyone looking to immerse themselves in PF boots probably at least knows the basics of this band and is looking for "the deep stuff". With that being said, I nominate all of 1970 as mandatory listening, followed closely by all of 1971!
Seriously though, pointing new people at the BBC Shows, 1975 LA/Boston, 1977 Oakland and the 1980 MOTB tape should serve as an outstanding starting point for anybody. After listening to those, they should have a very solid feel for what it is that turns them on/off... and then they can snatch all of 1970/1971 ;-)
Off surfing with Linda, of course!