Like others the Spotmatic F. My first M42 camera was a Zenit E and 58mm f2 Helios, I wore it out quickly, but I did have my first newspaper front page photo with it, also my first magazine front cover. I replaced it with a Prakticamat and Pancolar lens but had exposure issues, it turned out the lens aperture never stopped down consistently, so a brief spell with an Edixa before finally getting the Spotmatic F for my 21st birthday.
What a difference the Spotmatic F opened doors, I used it commercially alongside a pair of S1a's, but sold them early 1980s as I needed faster changing bayonet mount cameras for work (shooting rock band live).
Now I'm back with a Spotmatic F and an SPII and an SP500, also an SV, I've almost got the kit I always lusted after back in the 1960s when a school friend was using his father's Pentax cased outfit. But I don't have the same directions it was more a case of seeing a well planned outfit.
Ian