Most of my pianos are small: Wurlitzer and Acrosonic spinets are very common, as are consoles and assorted uprights from the best to the worst "free" pianos. (Note: There is no such thing as a free piano any more than there is such a thing as a free kitten or free puppy.) Most of the little pianos are fewer than 50 years old and are in decent shape. I have tuned a few which had not been tuned since Grandpa bought it, right after he came home from WWII. I've had mouse nests bigger than softballs and live larvae as well as the odd black widow or dead mouse.
In the past 20 years, I have tuned, perhaps 5% grand pianos. The big surprise to me has been the number of Mason & Hamlins, specifically the Model A. I must maintain close to 20 of those, ranging in age from 1914 to 1954. I have fewer Steinway grands, only one of which is a concert grand, most being about 6'. I do tune many Yamahas, the largest C5's, and the smallest G1's. I enjoy tunng most of the Yamaha's as long as they are in a stableenvironment. One of them, by the way, is from 1950 and has been well-maintained.
One of my favorite pianos to tune is a 1964 Bluthner. I play it every week, and it holds tune remarkably well, in spite of much internal rust and a split soundboard.
A piano most interesting and challenging to me is a 1954 Grotrian-Steinweg studio which came from Switzerland to Minnesota and spent at least 2 years in a metal shipping container, altenately being toasted and frozen. Lovely sound, but it is very unstable.
It is rare that I cannot tune a piano, but I have refused when the harp is broken or when the need for repairs exceeds any potential value of the instrument as a playable device. I have, on occasion, suggested gutting the cabinet and either installing a digital piano or making it into a desk or bar. Some pianos should be put out of their misery.