My all time favorite pen for coloring and for planning are the Staedtler Triplus Fineliners. In a 0.3mm tip, these pens come in great colors, are easy in your hands and slide quite smooth. The ink is bold and it doesn't bleed on the PPP planner pages or smudge easily. For around $15-20, you can get a 10 pack of basic colors. There are varying color packs with a large pack of around 20 for more or a set of neon pens. I'd rate these pens a 10/10 for my favorite.