A new wallpaper every day, updates the wallpaper at midnight. What I like about it is the simplicity and ease of use, four themes to pick from with seemingly handpicked wallpapers, wouldn't have my backgrounds. Wish this was available for iOS...
Something fresh every day. Change channels for more. I use it on my Mac. Also available for Chrome/Windows.
I actually just stumbled upon https://wallcrave.com/ the other day and was pretty blown away by their selection of wallpapers. The best thing about it is how easy it is to search through them. Everything is very high-res and the site automatically downloads the image according to your device's resolution. Pretty cool when you have a 3440 x 1440 monitor like me and have a tough time finding wallpapers at that resolution.
For Windows PCs, it automatically updates the desktop and lockscreen backgrounds using the fantastic images from Bing. Quick and easy install, and takes very little memory, though you might want to uncheck some extras that it offers.