If I had space in my life for more retro-junk I'd definitely love to have a working DEC VT100 or Lear Siegler ADM-3A if I could find one with the tube in good sharp condition so you could actually really use it to hack code on... but they probably go for a fortune by now, and ... well I just don't have space. For a slightly less rare and valuable terminal, a Wyse 60 would also be a good option (unless I'm misremembering, the keyboards were very nice and you could absolutely work on one of those today). When I was a kid all the libraries had Wyse 60s as catalogue search terminals, and I also learned how to use Unix through one of those beautiful things.