As thetypewriterman said, the SM9 is the clear standout.I have all three  of these machines.

1958 Groma Kolibri looks beautiful, but has a heavier touch than the other two. If the platen rubber has hardened over the years, as it most likely has, then this machine will sound loud.

1981 Lettera 32, I bought it brand new back then and it churned out a zillion school assignments. I thought it was a great typewriter (it really is), but somebody once described it as if it was 'filled with mud' when you type on it. After I read that, I couldn't shake that description. It has a slightly sluggish feel to it compared to other machines that I've used.

1966 SM9 is a standout. Very snappy action to the keys. Not sure if a '75 model has similar construction, but if it does, it's the best of the three that you mention.

Another worthy contender if you want snappy keys is a mid-'50s Smith-Corona Silent Super. Might sound a little louder than the SM9, but you could write for days on it.
You could probably pick one up (in the US, at least) for less than a hundred bucks, possibly even half that, but I would get it serviced by a typewriter repairer - they still exist - if I found one for under $100.

Good luck with your search!

M. Höhne wrote:

Of your listed choices (Why are you limited to those?) the only one that comes close to meeting your requirements is the Olympia SM9.
However, the typewriter that comes much closer to meeting your needs is a later IBM Selectic, a model II or III (consider the various models for additional features that you may appreciate).

Only one available to me in Denmark (for a decent price). I have no interest in electric typewriters.
 

Uwe wrote:

No one has an interest in electric typewriters until they use one, particularly a Selectric. 

My first choice for 4+ hours of daily typing would not be a portable typewriter, but a good standard. However, if you have to limit your choice to one of those three portables, there really isn't a choice: The Olympia SM9 is the only model that comes close to meeting your needs. 

Then again - it can be argued - there were writers who were known for using ultra-portables. Günter Grass and Gore Vidal, for example, used Lettera models.

There is also an offer on an Olympia SG-3  (10 Dollars), but the machine seems gigantic and I don't know if my desk has enough space. Other offers i got today.

- A Triumph from 1963 (40 Dollars).
- A Brother Deluxe (40 Dollars).
- An Olivetti Studio 44 (40 Dollars)

Should i consider any of them ???
 

The SM9 is still the choice, although I'd also be happy with the Triumph. [If not the SG3 or Selectric :-) ] The prices asked are all so close that They would not factor in to my decision. They're also all decent prices. Really, you're not going to get significantly better than the SM9 anyway, so don't let it get sold out from under you.