My favourite WordPress theme is Generate Press.
Why I like this theme is that it is a great foundation theme that you can develop and change to use for more than one WordPress site. It is so dynamic in how you can work with it that the sites can be created to look completely different, though have the same basic building blocks.
At the time when I started to use it about 3 years ago, I added 5 premium plugins from Generate Press so I could change colors, fonts, spacing and more.
So what is your favourite WordPress theme and why do you like it?