Let's say I wanna make a website that would allow a user to download a wallpaper in sizes for PC, HD, mobile and tablet.
What are the top used / best image dimensions I should host?
Common sizes for desktop are 800x600, 1024x768, 1280x1024 and 1600x1200
HD usually means 1080p nowadays so that is 1920 x 1080.
And this Google Browser size diagram may help