The pen tool is what I use for the line art. It can be a real pain but once you know how to work it it can be your best friend. I looked up tutorials on YouTube and just forced myself to do all the line art for one picture with it. By the end of that picture I had a decent enough understanding to start using it as my normal line art tool now.
Yes, when i was young and started with photoshop, i was REALLY mad i could never keep the paint in the strokes, nor i could make the strokes good enough, I now found out the trick to do it , and that is to KEEP doing it till your strokes are perfect ! did you know i always thought there was a secret smoothing tool to photoshop ? well, so i kept looking on youtube to try and find it, but no luck, lol turns out there wasn't even one ! XD