Folks have asked what I’m drawing my Inktobers with - the star of the show is definitely my Pentel Pocket brush pen. I can’t recommend it enough; there’s nothing quite like it. I also use a Copic Multiliner for very fine lines and areas requiring high precision/control.
The Pentel Pocket brush pen is a great tool for any traditional artist with its quality synthetic bristles and replaceable ink cartridges. I always pack it in my "basic bag," where I keep my most essential art supplies to bring on the go with my sketchbook. I have been using the same exact pen since I started working with it around 2011-2012. It takes a little practice, but it's a versatile tool and has results I can only compare to using an actual brush and ink.
Copic multiliners are great single width waterproof pigment ink pens. You can get disposables, but I swear by the silver-bodied "SP" pens as you can refill them and replace their nibs when they get worn or mashed down. They are comparable to Microns, which many are familiar with. I've used both and chose Copics just out of personal preference.
In case you're curious, the paper I'm using for this year's Inktobers is 140 lb cold press watercolor paper. I really like watercolor paper for ink-based pieces because of its absorbency (doesn't bleed all over the place) and texture (cold press lends itself well to the scraping/dry brush effects I use in a lot of my nature images).
We're about halfway through the challenge now! I hope you've been enjoying my drawings so far!