Originally posted by awscreo Is it the Pentax 100 2.8 WR? Or Samyang 100 2.8? Or the famous Tokina 90 2.8?
I haven't tried all of those, but I am quite happy with my DA 100mm WR. Very compact for what it is, great optics, and its WR. Some of the older Pentax 100mm primes have other features, like aperture ring or focus limiter, if you'd like those. I think a Pentax 100mm f2.8 macro is a great place to start macro, its a top lens with a very fair price (the recent few Pentax 100mm follow the same optical design).
But for "the best" you might want one of the legendary
Pentax 200mm macro or a 105mm Lester Dine. And the Sigma
70mm macro is touted as one of the sharpest lenses ever. I don't know how far ahead of the Pentax 100mm f2.8 macro those might be, but it fits my needs really well, even for non-macro photos.
Edit: Note that pretty much all macro primes from the last 20 years are really great at least in terms of optics. I don't think any of them are disappointing, you just have to find the focal length and price that you like. For beginning in macro its usually good to get one that more telephoto, like 90mm+. Wide angle macros like DA 35mm f2.8 macro are more difficult to use, because you are only a couple millimeters from the subject, and you might cast shadow onto it or scare it (if you are photographing insects)