I made myself two well-fitting sweaters this winter. The first was Chickadee, and the second was Shibumi, by Vera Sanon.
With this sweater, I learned why I need to use both horizontal and vertical bust darts. For starters, this is another top down sweater. When deciding which size to knit, I used shoulder dimensions. To accommodate my bust, I put increases into the plain stockinette portion of the fronts, and cast on at the underarms for the larger bust size. These modifications took my sweater from a size 48 at the shoulder to a 56 at the bust. These increases happening up and down the fabric are the vertical darts.
Now here's a handy tip I learned to decide if you need horizontal darts, usually added through short rows. Take a tape measure and measure down your back, from the top of the shoulder to the waist. Now do the same on your front, starting with the tape measure at the same location and ending parallel to the first measurement on the waist. If you notice a significant difference between these two measurements, you're going to need some horizontal darts. On a man's sweater, this may be on the back, to accommodate their shoulder blades. On some women, these may need to be distributed throughout the front of a sweater. For example, on a small busted woman who has a larger belly, the extra fabric may be required lower down.
Here's another way to see it. Ever had a shirt ride up in the front? I have. And it's because both the front and back of the shirt have the same length of fabric. The shirt looks great laying flat on the table, but I'm not flat. My body's dimensions aren't the same in the front as in the back. The fabric travels further at the front to cover my bust and so it rides up when I wear it
Again, working the sweater top down made it very easy for me to decide where to put the short rows and determine the fit. Here I am trying on the work in progress.
If you are looking to make a sweater that fits, the latest and greatest guru on the subject is Amy Herzog. I've got her Craftsy class and I highly recommend it. The only point we disagree on is top-down versus bottom-up construction. Amy strongly advocates for constructing sewn, bottom-up sweaters, claiming the fit and wear is much better. It may be true and the only way I'll know for sure is to try to knit a sweater that fits from the bottom up. It may just be my next sweater project...
Oh, one more farewell shot of Shibumi. Here's the pretty patterning on the back: