Best third person:
I say depending on what you like with third person shooters.
If you like being the sniper and shooting from long shots: Sniper Elite V2
Tactical as in being the Section Commander of a group: SOCOM Special Forces
Futuristic/ Interesting Characters and Weaponary: Resistance 3 or maybe even Killzone 3.
I know people are also enjoying Mass Effect 3 but admit working on Sniper elite V2 at the moment!!!
Hope this helps.
First person is where you play as the character - you'd generally only see the guns / fists etc.
Third person is where you can see the character - Nathan Drake style.