When I started out in science I used LaTeX with the a0poster package. Which gets the job done, but produced a bit boring posters. At some point I used Scribus

When I started out in science I used LaTeX with the a0poster package. Which gets the job done, but produced a bit boring posters. At some point I used Scribus but wasn't entirely happy. If I'd still be in academia, I think I'd look into Inkscape, heard mostly positive experiences from people using it.