Ranked in these QuestionsQuestion Ranking
Pro Incredibly lightweight
Pro Beautiful interface
Some greeters such as the Unity Greeter look absolutely beautiful on LightDM.
Con Not really lightweight
How lightweight it is depends on the used greeter, but they all require much more dependencies than other lightweight greeters like XDM or SLiM.
Con No Wayland compatibility.
This means no wayland session can be launched at all using LightDM.