I have a thrashed Royal HH which still works great, and that´s a good indication on how sturdy they are. But if I had to choose a typewriter to work with and one manufactured in the last 50 years (following the original question) I´d go for the Olivetti Linea 98. This is much of a personal choice, because it´s the typewriter which better suits me. It can endure heavy workloads, it´s definitely fast, comfortable to use, slightly smaller than the almighty Olympia SG3 (which is equally great) and here in Spain it´s ultra easy to find at a ridiculously low price.

The big problem with the SG1 is availability. I´ve never seen one and I want it!