Every set of armor you can forge in MH3U has a "Defense" stat. Arzuros armor sports a higher defense than Jaggi Armor, and Barroth Mail sports a defense higher than both.
However, all armor can be upgraded, which increases its "Defense" value. One of the NPCs in Moga Village even mentions off-handedly, "If you like the look of a particular armor, why not upgrade it and keep it around?"
So a couple of related questions: How many times can I "Level" a particular piece of armor? Is there a cap on defense? If I find a particular combination of stats / appearance I like (say… Ludroth armor), will it always be a decent option, or will higher level armors (within the same Rank, anyway) eventually totally eclipse it?