Hi Henry,
I own the 35mm, 45mm, 55mm, 80mm, 150mm, and 210mm, plus the 120mm macro "D". These are all of the previous generation (except the macro "D", of course), though all are AF. I say "previous", but in the case of the 35, 55, and 210 they are also the "current" version.
All are "good" though the 35mm is a bit softer than others (corners), as is the 45mm. The 55mm, 80mm, 150mm and 210mm that I own are pretty darn nice, though I would much rather have the 150mm f/2.8 "D". It's a very nice lens for much more money (and size and weight). The 80mm "D" is likely better than mine too, but my legacy 80 is very sharp. I'd prefer the on-lens clutch of manual focus control of the new "D" version. The 55mm is an excellent lens with good contrast, color and acuity. Most people seem to praise this lens, and I'm very happy with mine.
The 120 macros have a rep for being very good in each of their iterations, especially the last two.
The 45mm seems to be a bit of risk if you are fussy about corner sharpness, but I'm hearing and reading that the new version ("D") is also showing copy to copy variation and may be "iffy".
Jack mentions that there is some variation in the 210's too, but mine is very nice and I have read of mostly very favorable feeling regarding it. In fact, Jack's report of variation was the first that I had read of regarding the 210. I'm sure that his report is accurate for those copies he tested.
So, if one wants to shoot Mamiya without shooting the newest, expensive glass, there are some great values on "pre-D" models. Even the 80mm f/1.9 has a fun and sort of "dreamy" look, and can be had for just about $250ish.
I should add that I'm using my Mamiya with a Phase P25+ which tends to be kind to glass, and not using it wide open in most cases because this kit was put together for landscape mostly (couldn't justify a P45+ at the time). I shoot some shallow DoF stuff, but not so much with this kit, so I don't do a lot of shooting wide open with it. From what I've seen, the 150mm f/2.8 D has very nice bokeh – better than the older f/3.5 version, but the older one is not "harsh". One can also shoot hassy on the Mamiya (via adapter) for some other options as well.
In a better economy I'd get the 150mm f/2.8 D for it's character. And I really need to add the 75-150mm D for some landscape, but that's on hold too. The 75-150 would save me a lot of hassle in the field, so that sits highest on my list.
Others will surely have lots of info to share. I hope this is in some way helpful to you. Feel free to ask specific questions if you like.