First of all, there's no right or wrong pen to outline your art! I'm a firm believer that you don't have to have expensive/fancy art supplies to get a good result. <3 If you enjoy using Sharpies or Felteez, and you like the final product, then that's all that matters.
Personally I'm a bit of a pen hoarder so what I use varies. But most recently I've narrowed it down to only two pens: a tombow 62038 Fudenosuke brush pen (the "soft" variant) and a very tiny copic multiliner, just for small details. But honestly, the Tombow is a really good go-to, it can do both very thick and very thin lines. For instance I lined this with the same pen: blood warning But I have super shakey hands, so I prefer using the Copic for small details, just because it's a little easier to control the pen trajectory. The Tombow also comes with a second pen, which is the same but it has a firmer nib, but since I have joint issues the softer one is a little easier to deal with when you're inking for a long time! I do also use Sharpies to fill in large areas with black, since it's a lot cheaper to waste Sharpie ink and filling large areas in tends to wear out the nibs of the Tombow.