All of the Pentax 6x7 (Takumars) and modern-era SMC Pentax 67 lenses are old German Planar (in the case of the 105mm) or Distagon designs, excluding the two top-drawer optical performers (and noteworthy departures from standard Pentax optical designs), the 75mm f2.8AL and the impressive 300 EID. Neither of these lenses have a carry-over 70s optical construction to them.
There are noted variances among lenses (many are tack sharp, some are soft, some are uniform), the most notable being the 90mm f2.8, 45mm f4 and the 55mm f4. The evergreen 105mm has always had a consistency about it to make it a crowd favourite. It was also the standard lens that was included as a 6x7 (Takumar) or later SMC-P 67 “starter” kit, and legions of photographers got by with nothing more than just the one lens.
Of the 45 and 55 “shorties”, there is very little to set one above the other in practical use, putting aside critical examination of performance through known variation. The 55mm is the oldest design and is noticeably bulky and somewhat slow in terms of focusing (and also has the greatest number of reports of a loosening focusing ring, as mine did). The 45mm is a bit smaller, more comfortable to handle and, as others have pointed out, is a near-ideal landscape/scenic lens. The f22 aperture is not an issue with the inherent depth of field.
The disadvantage with these (and other) lenses is the f4 aperture, which makes precise focusing fiddly in low light, but very especially with a polariser; many, like me, get past this with a right-angle finder or the central-spot magnifier for critical focusing. Or take the POL off for focusing, and slap it back on when done. In essence, your kit should have a couple of fast lenses to get past the circumstantial failings of f4 lenses.
The 55mm f4 came with my 67 (it had a slightly loose focusing ring). After 12 months, I ditched the 55mm, as I preferred the lighter, wider, smaller and more agreeable 45mm f4, even if the filter size was “out there” at 82mm! I print very big from all lenses (and I have unflinching 100% tripod use). I too have the 90mm f2.8 and the 165mm leaf shutter lens (a sharp and worthy performer in its own right, if a bit on the heavy side). The leaf shutter lenses are novel, but have idiosyncracies which must be observed; case in point: the 90mm LS can be used with mirror lock-up on those bodies equipped with it, but the 165mm cannot. The potential for damaging the lens and camera shutter mechanism is omnipresent with the 165mm, not that you aren't given sufficient warning in documentation for this lens.
If you want images of the very highest quality (combined with refined shooting / stabilisationn technique – not necessarily any variation of handheld), the 75mm f2.8AL with a deserved almost cult-status, provides optical refinement of several orders of magnitude above its many and varied stablemates. The downside is the cost (on an upward trend on the used market, around $800 to $1400 for a mint/NIB with papers specimen). The compact size, very precise, “pinky” focusing, spring-loaded aperture ring with half-stops and easy low-light focusing are big pluses if much of your work puts you in challenging lighting. True, the 90mm 2.8 could also be used, but it is not in the same league of nimble handling and optical refinement. The case being? Horses for courses and take your pick!
Getting the “right” lens kit depends a lot on trial and error and experience.It is very fortunate that the rise of digital photography has had an unexpected positive effect on analogue: medium and large format are today much more affordable now than they once were e.g. a Pentax 67 and 105mm would have set you back more than $5,000 27 years ago! We've got the big easy. It is fun to build up an humungous 67 kit — a real film camera with terrific performance and one that makes as much noise as a door slamming shut (this is great for scattering stickybeaks!). Just be aware that the more lenses you add, the greater the pain in the back and legs...
Postscript: Get yourself a lightmeter. The 67 TTL prism is rudimentary in its analysis and meters only to 1 second (its accuracy is also affected by age). If you are shooting in early morning and evening, a separate light meter is well worth considering.
