It even depends on the type of PvP you are doing, in my opinion.
I like to match up my elemental armor for PvE, one Anti-Eart, one Anti-Fire, one Anti-Air and one Anti-Water.
In 4vs4 I would suggest Fire and Air resistance at the moment, being that they are the prefered ele classes at the moment.
In the HoH/ToPK you might want to bring those two and and maybe even anti-earth to combat against KD warriors. That's my observance, anyway.
But in my opinion, the Hydromancer's coat is the best looking
BTW: Many make the mistake of getting armor specific to their used attribute. This is a big mistake, it's like naming your healing monk "Healing Healer [Please kill me first]": it's painting a bull's eye on your head.
Naturally people will go after the areomancer before the hydromancer.