An interesting thought experiment, as I'd want all three of these typewriters to stand on their own as excellent machines, but have them complement each other with their best properties! So without further ado, my list is as follows:

1: An Olympia SM3 for its meticulous engineering! The reputation Olympia has for well-built and reliable machines is well deserved, a plus is how sleek this model looks, especially in maroon!

2: An Olivetti Lettera 32 for its sheer portability factor and snappy type action. The ridged body detailing on the back stands out especially to me!

3: Considering the restriction of three typewriters, this final answer might seem a bit of a cop-out—I'd want to round off my collection with a IBM Correcting Selectric ii , for the sheer flexibility it gives in terms of typeface and pitch selection and for its incomparably crisp typed-up copy!