Ok - I tried a test this lunchtime - I took a predrawn picture, and tried to ink it in 20 mins, 3 times using different software. Firstly, Manga Studio - now I DO like this program, but it's always a pain getting the settings right. I've found that to get a good inked picture, you have to ink a 1200dpi, and reduce down. Today I took the default settings (600 dpi) and realised my mistake, as the picture was a bit jagged. Secondly, Inkscape - worked well, quite quick, but wasted time on fills - really annoyed me that - but good overall, and slightly better than MS. Lastly - Xara X1 (soon to be replaced in my arsenal by Xtreme 4.0) - worked well, output great. Although It doesn't respond to pressure as well as the other two, I still managed to get a better looking cartoon (and completed more of it) than the other two, mainly because the default line in Xara is better.
Xara then, won by a small margin - we'll have to see how Xara Xtreme does!