need help about the conception of IoT , LXQT, LXDE

Hello everybody:
When i update my system of my BB-B board,i should download the .img file.But when i download the files,i don’t konw the difference between IoT , LXDE and LXQT.

So what the difference about them. In addition, i want to use a LCD screen as a peripheral device, what version of the .img file should i download.