Red side Best side!
Ahem.
Now that that is out of my system... 😄
Red side has always had lower numbers even way back when it first went live. There may have been peaks ever now and then, but overall, Redside is lower. Which is a shame because the writing is so much better on Redside.
If you want to be one of the norms, one of the crowd, and tag along, go Blueside.
If you want good writing, go Red side.
If you want to mess around with morality, go Gold side.
Goldside - Tell me who's right and wrong over there. Most people are lazy and can't be bothered picking a side. Even through the writing is excellent and who you think you can trust may not be the case.
Redside - You build your way up to power to rival that of States/Recluse, and have fun on the way. Where else could you take down clones, pit Arbiters against each other, BEEEEES, pretend to be a good guy while working for your own causes, and Mayhem Missions.
Blueside - Teaming, bright designs
When it came out CoH was meant to be played as a team. Yes you can solo, but its funner as a team.
Look at CoV and the archetypes that rolled out with it... they are basically suited for duo or solo. They team for convenience.