I am a layperson for astrochemistry but IIRC comets have much higher hydrocarbon content by an order of magnitude or more (and obviously more water, fewer metals to contend with for extraction energy requirements).
Anyone have more insights? Did I miss mention of comets in my skim of the paper?
Ps usually HN not a punfest, but kudos for the Starmite(tm) @andai
I think comets are significantly harder to get a hold of; they're in long-period orbits, and changing their trajectories - or even catching up with them! - is significantly harder than catching something that circles the sun inside the orbit of Jupiter.
But could you use the hydrocarbons on the comet as fuel to change the orbit to a desirable one?