Actually Illustrator was the package of choice at the start and many of the core parts are in Illustrator. Then it became not free anymore and we changed to Inkscape. I'm a late comer and haven't used anything but Inkscape but the older folks in here should still know illustrator I expect. I'm working on correcting my pcb svg (the bottom connector was .1 too high) and adding the board outline and mounting holes to silkscreen from the eagle svg. I'll post it when I finish. PS. you may want to use Inkscape .91 (one version back) as .92 has changed the resolution from 90 dpi to 93 dpi and I had scaling problems on a part (but only that one part for some reason) using .92 and so switched back to .91.
Peter