I know I'm late and its all been said but tough.
On this difference in the brothers' armor...
Faramir, and that of his command which were the Rangers of Ithilien were prepared to move quickly and quietly in the woods of Ithilien setting anbushes and such and doing their best at not being seen or heard.
Boromir on the other hand commanded the garrison of Osgoliath and so he and his men had the full battle armor that would come in handy in the direct close-in fighting.
Later, when Faramir and his men was summoned to Osgoliath as emergency reinforcements for the Osgoliath garrison, they wouldn't take the time to get 'suited up' in their armor (which Faramir later did for his suicide ride from Minas Tirith).
Also, when Boromir went to Rivendell, he was dressed so:
More suited for travel, but still quite functional.
And then you have their own personal preferences of adornment.