I have found a solution here.
So for my case, I created a new xsession file:
/usr/share/xsessions/smart_de.desktop
[Desktop Entry] Type=Application Exec=/usr/share/startDE.sh Name=Smart DE change Comment=Awesome for user1 and LXQt for others
and a script that launches a special DE for each user:
/usr/share/startDE.sh
#!/bin/bash if [ "$USER" = "user1" ]; then exec awesome else exec startlxqt fi