Support for the 16-bit pic24/dspic33 parts is one of the nice things about Positron.
But, if you thought SF was a bit quirky Positron is possibly worse in that regard.
As you say, each have there own strengths and weaknesses.

As far as the 18F Q series goes, it only supports the same parts as PBP does (Q10, Q43).
That's an MPASMX 5.87 limitation, and neither PBP or Positron can do much about that.