When comparing CDM vs Qingy, the Slant community recommends CDM for most people. In the question“What is the best Linux Display Manager?” CDM is ranked 3rd while Qingy is ranked 16th.
Ranked in these QuestionsQuestion Ranking
Pro Has almost no dependencies
Pro Supports virtually any DE/WM
Pro Very lightweight
takes up near no system recources.
Pro Getty replacement
It is a getty replacement so it will not only replace your X11 login manager but also your getty.
Con Bad availability in distros
There is no CDM in distros repositories (only in AUR on arch)
However you always can compile it from source.
Con Curses-like interface
Very simple and minimalistic graphical interface.
Con Ancient fossil dredged up from nearly a decade ago
Qingy doesn't appear to have updated since 2010. That's a long time in Internet years.
Con Not a display manager
Qingy is not a display manager - it is a getty replacement.