Originally posted by Edmund So my choices are really just the Macro or the Macro OS HSM. I am guessing the plain Macro version may provide the best results (based on reviews and users' opinions). I am still open to other's views on this.
They both are "macro" (more precisely, close-focusing). The non-OS has a slightly better magnification ratio, as has already been mentioned, but it's not likely to make a big difference in practice. Neither is the f/4 vs f/4.5 aperture at 70mm.
What it boils down to is if the difference in price is worth having OS and HSM. On a Pentax body with SR, and in that focal range, I don't think OS is worth it. As for HSM, I have not tried it, but I own the non-OS version and it focuses quite quickly.
Conclusion: I would recommend choosing the older non-OS version.