Server barely matters anymore. I'd say the only differences are:
- RP vs non-RP realm;
- Crafting orders are still realm-specific but that doesn't matter to F2Ps;
- BOEs in the AH are still realm-specific but again, that doesn't apply to F2Ps;
- The group finder is still realm-specific but that doesn't matter either.
Is there anything else? Because guilds are now cross-realm. You can freely trade cross-realm (again, not relevant to F2Ps).
Let's talk about the RP vs non-RP thing.
RP realms are still separated from non-RP realms in terms of sharding in the open world. If you're on one, you won't naturally see someone from the other when wandering around. You can invite a non-RP into an RP realm and vice versa.
Why does this matter? Because it's better for hunting rares in the open world... generally. Chromie Time on, Warmode on on an RP realm and you likely won't see anybody.