Just to muddy the waters, I thought I'd throw my experience into this discussion. I use the 140 (the macro lens) as my portrait lens with the RB and I really like the results.
I got the 140 rather than the 150 for it's quality as a close-up lens, but I've been thrilled with the results I've gotten from it as a portrait lens. When shooting anything but close-ups I just leave the floating element at infinity...and the results have been great.
I haven't used the 150, so I can't compare the 140 to that lens, but I found that I liked the 140 more than the 180. Just a personal opinion though...your mileage may (and probably will) vary.