What’s the difference between GDM and LightDM?
I'm a somewhat experienced noob on this Linux-thing. I'm growing quite familiar with Ubuntu and I just love Gnome(3+).
Just by accident I was presented with a choice the other day. I was upgrading from an old Ubuntu version and then I had to choose which display manager I wanted to use with the new version. Throwing the dice (even numbers = LightDM, odd numbers = GDM) I got a five, hence, I choose GDM.
I have a rather decent machine (AMD Phenom II hexa-core processor @3.2GHz, 16GB RAM, too much disc space, generic on-board graphics card). I'm currently running Ubuntu 12.10 with Gnome4 (yes, I know, I'm brave/stupid, considering the fact that both are still in beta stage). The machine has a quite central role in my network, but is almost exclusively connected to from other Linux devices (considering Android as Linux).
Basically, I just want to know which manager is the most optimal for my above mentioned system (if there is a difference at all, but there is a reason someone wrote LightDM, right?).
Are there any performance benefits or compatibility issues to consider?
Will I notice a difference using one over the other ?
Remember I'm a noob, I barely know what a display manager is or does.
P.S: I don't want to start a GDM vs. LightDM war here (I will delete the question at the first trolling attempt).