Believe there's been a similar post like yours but anyways. Sometimes it can be hard to find groups but sometimes its easy it sorta depends. If you play after midnight on a weekday it will be even harder for ya. I usually only get to log on at around 11pm gmt on weekdays and at that time its hard to get a group. Luckely i have a couple of SG members that don't mind teaming with me for a few hours before bed.
Personally i found the US servers more populated when i played there. Not sure how many players play on Union & Defiant. I'm sure someone else here can answer that question.
Hope you get the answers you're looking for. Best bet if you do decide to play defiant or union is to find people that you enjoy to play with and that play at similar times as you.
Before COV launched if I did a search on Defiant there were usually between 600 and 700 players playing of an evening. When COV launched that dipped down to between 200 and 300. Recently when I've searched there have been around 400 playing. The few times I took an alt for a wander on Union back before COV was launched there were > 700 players playing but I haven't checked since then.
Edit: This refers to hero numbers btw - I have no idea how populated the villain side of the servers are
Defiant 50�s: Generalissimo, Righteous Bob, Splortch, Brutus Cayuga
Union 50's: Chimera Obscura, Diet Anthracite, Grim Proctologist, Puny Little Minion, Raging Bitumen
In Soviet Russia, mission farm you!
Gens stats are about right.
Around 500-600 villains at the busy time of the evenings from what I remember.
I've started using Global Chat to LFT on heroes. Villains it's easy to get a team.
*Edit* : An SG could sort your teaming issues, assuming they aren't all off villaining. Also if you find a few good people ask them do they mind if you Global Friend them.
Well of course you're going to have a hard time finding a team at midnight, the only players online are night crawlers like me 
However the amount of players is spread out between CoV and CoH, meaning it WILL be harder to find a team.
basically all above is true , but there are ppl on that time of night and if u can make a few freinds to team with regular then its not so bad.
/has_been_recording_and_therefore_AWOL
should be back nowish.
Plight
i just wonder how many people play on defiant and if you find the population being on the ok end or the lacking end.
i believe i came from a more populated game where i could find a group at anytime of the day.
im just used to being in the hollows all the time so i cant really tell about the rest of the game but im always having a hard time finding a group after midnight(GMT +1)
what are your guys view on things?
how much different is defiant and union population wise?
i know a some of you started on the US version and transfered to EU when it came out, how is the US population compared to here?