|ElvUI was once based on Tukui but has since gone through a complete overhaul of not only design but also file structure, UI features and the code itself. The look of the UI still mimics that of Tukui in the way the visual aspects (panels, borders etc.) are presented.
ElvUI is designed to be more user friendly than Tukui by providing an elaborate and easy to use in-game GUI which allows you to customize just about everything without having to reload your UI between changes. Extra features which isn't included in the default UI comes built in with ElvUI. Install guide during initial login will setup your UI to match not only your screen resolution but also your role (Caster, Physical DPS, Tank, Healer).
ElvUI is perfect for those who wants a good looking UI which doesn't require lua knowledge and has a lot of features built in. ElvUI is less memory and CPU friendly than Tukui.