Hi from Portland!
First off, your da50 f1.8 and a macro lens are completely different beasts - the focusing of a macro lens has a much much longer throw which can make AF quite a bit more difficult and slow. In low light conditions and for portraits, the f1.8 will come in handy too.
I've had several for Pentax over the years: Sigma 70, Sigma 105, Pentax DA35 macro, Tamron 90, Pentax DFA50 Macro, and DFA100 Macro WR. All of them were great and were extremely sharp with only minor differences in color temperature and bokeh. Personally, I found the Sigmas too big, particularly with the hood arrangement that they have - image quality was awesome though. The Tamron I liked, but I like the feel of the Sigma and Pentax 100 better. Focal length wise I liked the 100 for really tight shots, but found the 50 and 35 ok but often my working distance was very short. My fave out of all of these is probably the 100 WR followed by the 35. The 100 has a punch to the images and it's small and weather resistant. The 35 is super small, has great color, and is excellent from macro to infinity. Build quality of both of these lenses is superb.
Here are some macro's I've taken w/ these lenses and with others (often old lenses with a extension tube):
https://www.flickr.com/photos/55038128@N00/sets/72157643447729933