I love to transform my OS into macOS so, for me, vinceluice's McMojave is a must have. I use it with a custom icon theme (made by completing Mojave CT icons with other icons from La Capitaine, for example). That being said, I'm aware it's not for everyone.
Apart from that, I'm a simple man: Adapta and Arc are amongst my favourites. I also like Pop but it's unfortunately not Budgie-compatible. As far as icons go, Papirus is my go-to.