I tried 3 of them.
There's no difference.
LED Sucks
Mercs rule out people who suck at combat
EC is ok
CMG is ok
FDC is organized and fun to be in
BoS is fun to make drugs and sell
GoM is one that I don't know about, ask chex about them
VC is an ok faction
And there is a loving difference, I've played almost all the factions, if you like organized stuff then join FDC, if you like ganking join the mercs, if you like production join EC, CMG, and VC, if you like making drugs and fighting alot join BoS, if you like jailing people and using stun guns join LED.
And please tell me the factions you tried