General consensus seem to be:

• Aether: Raiding.
• Primal: PvPing.
• Crystal: Roleplaying.

The reality however is:

• Aether: Mind your own business and become the nastiest human being when someone mentions your DPS or inability to do a speed run.
• Primal: Nobody really talks about you, so you're kinda just there.
• Crystal: "Ya'll casuals suck. Learn not to be so bad. I'm transferring to Aether.".