Now seriously, use the Ink tool on GIMP, it's the best thing I have ever seen! Considering you want a vector clean look, while keeping your lines lively. If you really want vectors, then why the hell are you using GIMP? Use Inkscape or something!
Why this? Because I think most people don't know the existence of this tool and because the only tutorials I see around here are about the path tool.
Don't use the path tool UNLESS you have pretty good reasons to do it, and lineart ain't one. Many people complain that their sketches look more lively than the final lineart, and using path tool is the main reason why. When using the pencil you're doing the natural gesture of your hands and arms, if you remove that factor you get a really dull and perfect line. Perfect lines don't exist and your eyes tends to notice that in a negative way.
Using the Ink tool will keep your lines clean, open for pressure, and your gestures. If you do a bad stroke or see any huge imperfection on the line, or even if you want to thicken or thin it, use the eraser! It's also a nice tool for you to use, because as in tradicional art, you don't have to get it right at first! (Unless you're using a pen for example)
You can always say "Screw that! I'mma gonna use the paintbrush with my own settings, loser!", but be warned that getting this kind of line with it is difficult. The best comparison I had was when making this: [link] The skull was first made with the paintbrush, then I moved to the ink and the result was on sight. Sincerely, as much as I tried to fix it, I can still see the flaws of the paintbrush on the finished result.
Credits go to who told me about this tool right when I was making the above picture. My first reaction was "This is exactly what was missing in this picture!". USE THIS TOOL DAMNIT!
Unless you use Photoshop or any other program. But if you use GIMP, try the ink tool and then dance to this: [link]
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TL;DR version: TRY THE INK TOOL OUT AND FIND OUT IT'S THE BEST THING EVER AND THEN DANCE TO THIS: [link]
Yes true, but filters can only be used if you have a clean pencil lineart, and it still it won't have the same effect as the ink tool. It really depends on what you want in the end, and for the kind of lineart that most people do (aka. sketch and line digitally), the ink tool should really be used.