well considering the fact that altcoins doesn't have that much real world usage, and also the anonymity that bitcoin offers (as long as you don't link it with your bank account) bitcoin is the easiest way for darkweb.
the question here is what percentage of bitcoin usage is in darkweb?
I think 30-40 percent of users of bitcoin spend it in darkwebs,market in dark web is much alive with the use of bitcoin,theres a lot of money being transacted there day by day.