Re: PIC16LF1937 or Newer Pic
If you're choosing a new MCU, I would go with one of PIC16F1xxxx - they have new periphery, such as logic cells, allegedly better layout of SFRs etc.
However, PIC16F1937 is already a newer design which solved many problems common to earlier PIC16s. Therefore, if you want to keep it because you re-use a large portion of your existing project, there's no compelling reason to switch to PIC161xxxx.
Also, dsPIC33 are much more advanced and fast PICs, many of them specifically designed for driving motors. Although, it is probably an overkill for the job.