For an average illustration/comic, I generally use a size 00 to size 4 brush to ink 75%-85% of my drawings, then I go in with a nib to finish things off. The size of my brushes are proportional to the size of my drawings.
When it comes to inking, I am not very particular about the a brand of the brush, as long as it’s a round, synthetic or sable brush that is not over $5. The reason for that is because I am a total dick to my brushes, and I tend to destroy them very quickly. Expensive, fancy brushes only last minutely longer than my $4 for 10 China-made ones. You do the math, but I think I save money.