It's quite the rabbit hole with different answers depending on your preferences and style. Many of the major brands exemplify a sort of peak in industrial manufacturing that is not seen in today's mass produced appliances. I especially like Olympia from the 50s, 60s, and 70s which are Germany made and blend excellent build quality with a simple mid-century modern sorta style. Some people enjoy really old stuff like an Underwood and others prefer fancy electric machines like the IBM Selectric. You can't go wrong with brands like Smith-Corona, Remington, Royal, Hermes, or Olivetti though there's many more to discover!