SMC Pentax 67 lenses have a higher degree of refinement (coating and element design) over the Takumars, even though they are based on old Biogon and/or Distagon optical layouts. A few are true stellar performers and still command a big price (and weight). There are maybe only two Takumars that really surpass the later designs of the SMC Pentax varieties. Pentax was on a winner with most of the lenses and limited only by the technology of the time.
I cite the 45mm, 55mm, 165mm, 105mm and 90mm SMC Pentax 67 (the modern naming for the lenses that came out from 1989-1990 onward) lenses as examples of the best of the best. They are regularly found at auction or pro-level second hand dealers, but should ideally be inspected by hand for faults such as dust/dirt, scratched rear elements, bent or broken aperture coupling lever, deep scours of the mounting flange, jammed aperture ring, damaged front filter threads (or bayonet filter engagement nibs) and fungus — a lot of these things can be found during routine inspections; rough treatment by professionals is usually par for the course for these big and very well built lenses, but a surprising number I have seen have been in terrible condition (and advertised as "Mint –"!!). My favourite lens is the squat and easy handling 45mm; I really should be getting prints around 1m across from it, only that the budget doesn't extend that far...
I wouldn't necessary shy away from the old Takumars, apart from my dislike much earlier on of the rather unfriendly knurled feel to them. A number of lenses also had thorium rear elements which should liven up your conversation if you start talking about a pale yellow tinge!