The 129 better player uses both: paper for technique practice, digital for time trials and X-Wing/Swordfish practice.
Alternatively, in speed-solving communities: sudoku 129 better
Only pencil mark candidates when a number is restricted to two (or sometimes three) spots in a row, column, or box. This keeps the grid clean and highlights the critical "decision points" where the puzzle logic lives. The 129 better player uses both: paper for