Great, thanks guys - yours answers are helping me to decide which is better:
- Craftworld Harlies (2D6 sight to shoot them, but has to use a warp charge)
- Dark Eldar Harlies (Shrouded + Stealthed)
The Dark Eldar harlies require cover much more than the Craftworlders and therefore will end up slogging through difficult terrain. Thus the Craftworld Harlies seem to be the better option for an accompanying character whilst the Dark Eldar ones make a better solo unit.
"An eye for an eye leaves the whole world blind"
Mohandas Karamchand Gandhi