Wow! What a question!

Standard Desktop:  L.C. Smith no. 8 / Remington 17 (L.C. Smith:  because the decimal tabulator was really cool which is the main reason I purchased it; Remington:  a nice find/rescue from my parents' basement that I found to be a great typer during NaNoWriMo in 2015.

Portable:  Royal Quiet Deluxe (I have several of these)

Ultra-Portable:  Corona 3 / Royal Dart (Corona 3:  The coolness factor gets me on this one.) I can't make up my mind between the Royal Dart and the Smith-Corona Skywriter.  Both are reasonably good typers, though each one has individual keys that seem to stick.

JoeV wrote:

...if you had to start all over again with manual typewriters, and knowing what you know now to be the best brands and models, which machine would you choose as your primary writing tool?

Clearly this is a very difficult question for a collector to answer; once someone has been exposed to a number of fantastic typewriters it becomes practically impossible to narrow them down to just one machine. Proof of this can be found in the first few replies of this thread, each of which listed several models and ignored the requirement that there be only one.

To answer the question at face value, which is to select only one model to be used for writing, I would immediately eliminate every portable typewriter. There's no question that many portable models are great to use, but they don't match the feel of a standard, and given this is about selecting the best writing tool for the majority of the time, I would gladly sacrifice portability for a more solid platform.

Although there are a large number of standard models that I'd be content to use in such a capacity, I'd have to give the nod to the Olympia SG1. The most overwhelming reason for this choice is that it has the most user-friendly features for a writer, which for some reason most other standard models lack. As a writer I want a paper rest so I can quickly scan what I've already typed and know when I've reached the last line on the page. I also like the four-position vibrator control because I want to use up the entire ribbon. And I certainly appreciate the quick detach carriage for serviceability and ease of cleaning. 

My choice was also tainted by the cushioned keys that spoil my fingers, but perhaps the most compelling feature on an SG1 is the paper injector. Once you've loaded a few hundred sheets of paper into a an SG1 and then switch to a typewriter without a paper injector, it feels like a real downgrade.


 

Among manual typewriters I own I would pick the Hermes 9 standard. It's an amplified version of the 3000 with comparable build quality, touch and imprint, and I like full sized machines. The film-ribbon sharp 12cpi print is uncanny given the use-indented platen and the inexpensive heavily inked ribbon. How does it maintain that print quality?

You did say “start over” and not “keep one”, so given that Hermes office machines do not show up every day I would first look for a 1950's Royal Quiet Deluxe while I was waiting. It's a great all around machine neither very expensive nor hard to find while looking for The One. If you removed the qualifying “manual” I might look for an IBM type bar electric. My copy of the model B is a serious machine which compels you to Think - the stern IBM logo gazing at you out of the green crinkle forbids you to trype! Only complex abstraction and analysis will do.

If I could only pick one, it would be a Royal KMM with elite typeface.