if looking on "main campaign" (Vivec) then I can say
EP - mostly zergs and RP players because of skyrim
AD - alos mostly just big zergs since zerg squad dominated cyrodil map can say long ago and many ppl switched to AD because it was winning alliance so also many casuals are here
DC - hmm, not zerging that much like rest, more faction loyal players as this alliance have nothing or just less reasons why switch to this alliance from another (like I wrote AD is now outpopulated because is winning alliance, EP have skyrim)
if looking on "main campaign" (Vivec) then I can say
EP - mostly zergs and RP players because of skyrim
AD - alos mostly just big zergs since zerg squad dominated cyrodil map can say long ago and many ppl switched to AD because it was winning alliance so also many casuals are here
DC - hmm, not zerging that much like rest, more faction loyal players as this alliance have nothing or just less reasons why switch to this alliance from another (like I wrote AD is now outpopulated because is winning alliance, EP have skyrim)
pffffffttttttt dc do nothing but faction stack
For me :
If you want numbers and no brain farming : EP
If you want big battles: AD
If you want small scale PVP : DC

@Morgul667 That's interesting. EP seems to be the same on PS4 but DC and AD are opposites. DC have loads of large a** groups and one zerg leader will even kick someone from his group if they don't put down a siege. AD is full of small scale or solo players which is why we are bad at defending keeps. lol.For me :
If you want numbers and no brain farming : EP
If you want big battles: AD
If you want small scale PVP : DC