Well, I usually use my Underwood #5 as my main desktop, but sometimes I use a Remington #10, or a Royal #10, etc. As for portables, I use those when I don't feel like typing in my room on a desktop and bring a portable in a different room, and usually I use a Royal Futura as a portable, but once I get my Corona #4 running, I plan to use that.

Keep in mind I have 20 something machines.

I do most of my typing--drafts and drills--on My Royal KMM, and use a variety of portables for typing letters, depending on my mood.

Other than that I will grab one of my SM9s when anything serious has to be banged down without fuss, it's usually a matter of whim. 

My typewriter desk now stores a nearly mint Royal HH, and though I am not impressed with its limited range of features, it is a very friendly machine to use and beautiful to look at (IMO), so that gets a fair bit of use.  I just love watching it rise out of the desk when I lift the lid, like Excalibur from the lake.

Another near-mint machine, an early Alpina SK24 is often chosen (apart from its innate superbosity) just because I feel so lucky to have the keeping of it. 

I have a 2-day rotation of the machines in my collection. 

That way, each gets used and looked after (if they need it) within each month.

I only have one (1) cursive-script machine in my collection.  That one gets used any time I will write a note/letter of a personal nature.

There are no non-working machines in my home.

My collection isn't large by the standards of some, but I now own more typewriters than I could have imagined after buying my first one. Right now I have 11 typewriters in total. (I was up to 12, but gave one away to a friend last week as I found that I just wasn't really making use of it.) With the exception of the two Smith-Corona Silent Supers that I own, every single machine features a somewhat different typeface, so that usually factors heavily into my decision of which typewriter I choose to use for any given need. I do use all of the typewriters that I own. If I'm going to be writing to someone with troublesome eyesight, I'l make sure to use one of my typewriters featuring PICA sized type. I personally favor the 11 character per inch typefaces as found on most of my European typewriters including a couple of the Olympias, the Facit and the Voss. I have just one typewriter that features an Elite typeface, and Underwood machine, and it is my least used typewriter. I keep it around in case I ever have a specific need for type that small. I have wondered if I'll some day get to the point where the only machines I'll use are those with PICA sized type simply due to my own degrading eyesight.

My favorite typewriter, and the one that I use the most, remains the first typewriter that I bought, a 1966 Olympia SM9. Were I to acquire many more typewriters then I imagine that I would also begin giving more away. I don't have any interest in hanging on to typewriters that I'm not making use of, I'd rather see them in the hands of someone else that could put them to use. If I could only keep just one it would be that first SM9 that I purchased. I picked a great typewriter to start with.