I started using PIC24/dsPIC33 (in particular the PIC24F's for their rich peripheral set) 2 years ago and am really pleased with their power and flexibility - they are pretty much all I use these days. I have used PIC18's occasionally due to the excellent Swordfish compiler which isn't available yet for the 24-bit core devices. They only time I used a PIC16 in the last 2 years was when the app called for a small physical package and settled on an 8-pin MSOP.