Health coverage after losing my job: marketplace or Medicaid? (update)

I have 3 weeks left on my current insurance and I am comparing options. I have been trying to stay organised about it. I think my income this year might qualify for a subsidy. How fast did coverage start?

Losing job-based coverage usually opens a special enrolment window, so check the deadline on the official marketplace site. I missed it by a day once and regretted it.