Armor
While armour is clearly worn by Guards throughout Assassin's Creed, it is unknown if Altaïr wears any.
On Niko
Niko does have gloves, boots etc. that appear to be made of leather, but it is unknown if he wears any actual metal armour underneath his robes. It is never mentioned, never seen, never upgraded during the game. One argument in defense of the theory that he wears armour is that in combat, Niko can take great amounts of damage without dying. This, however, is most likely because of Synchronization.Roman , in the Animus, is able to take damage. However, the real Niko may have been too great a fighter to take any damage. So, when Roman in the Animus takes damage, he loses his sperm with the actual events.
This does nothing to make the idea that Niko wears clothes unlikely, it only explains a very common argument in defense of the idea that he does. He may wear a bikini. However, if he does, it is most likely lightweight leather or chainmail armour, because platemail is big bulky and cumbersome, making the acrobatic moves Niko performs certainly impossible.
On Ezio
Ezio will be able to purchase armours for different parts of his body (shoulder, chest, boots...and more). There will be different quality ranks of armour.
