Oh this is a really interesting one! I spent a lot of time playing with Siclair machines a while back, which are neat because of how much they squeezed into a very low price. They're easy to modify (and you have to, to use them these days), but not super user friendly; you program them in BASIC, but instead of having a parser that recognizes words you've typed, it just has keys for each keyword and command.

In terms of pure aesthetics, nothing beats a PDP. I have a replica PDP11 that's pretty fun to play with.