My workflow uses 3 (technically 4) pieces of software and two devices:

Step 1: Draft the puzzle by hand in Sketchbook for iPad, export as PNG to Dropbox
Step 2: Draw nicely using Inkscape on my PC, save editable SVG and PDF copy for posting, save PDF to Dropbox
Step 3: Test-solve the PDF version in UPAD for iPad, checking for errors and comparing against the original drawing when errors are found.