Hmm, I was always fond of the designs in Aion and Blade x Soul, but I'm drawn towards games that like to use an 'angelic' aesthetic with wings all over everything. Winged swords and bows in particular. And since I play male characters almost 100% of the time, I liked the skin selection for them.

What I particularly liked about Aion though, was the spell books and orbs for the mage classes. It really had some gorgeous spellbook skins, and the skill animations/way you held the book really made you feel like a mage. I'll always miss that. This game is....underwhelming when it comes to the mage classes skill animations. But as far as crafting, housing, and other aspects go, ESO has more substance. Especially after Aion's lore was gutted from it.

Well whatever game that has armor that actually looks like armor, you know protective gear is the best looking armor.

Whatever these other games have is not armor.

BDO had some really pretty armor clothes. A lot of it was overly suggestive, but you did at least have an actual choice of good looking outfits that weren't just fan service. Most similar games (Korean, graphics focused, grindy, etc) seem to mostly have the grand choices of "over the top absurd armor", "XXX", and (maybe) some old gear, usually mid-level, that's hideous. It's not that I dislike the skimpy clothes, it's that I don't like when the only choices are to look slutty or like a low-res, low-poly blob.

I think my actual favorite, however, would have to be one that is far from the first to come to mind for most when talking about pretty armor: Guild Wars 1. Part of that owes to the design of the game and characters in the first place being appealing but still realistic, but the armor itself is widely varied, beautifully designed, and has fairly limited model reuse. (Gallery links are allowed, right? Links at the bottom to other classes, try Warrior if you prefer actual armor.) To top it off: You could mix and match to amazing effect! Within your class's armor anyways.
Guild Wars 2 could have topped this, it has some very pretty clothes with nicely done physics (or fake physics) for how the different parts of the clothes move. However most of their available armor looks like it was designed by and for 13-yr old boys. It's absurdly over the top, and doesn't even try to be appealing about it. The dye system, however, is the most astounding of any game period - MMO or not.

Secret World had some pretty nice clothes, but since the game was umm. Well, at the least I did not play it enough to appreciate its clothing options.

Since this thread seems unrelated to ESO...
ESO's actual armor is basically straight up disappointing. There are some nice textures, but the models are all extremely similar if not just outright recycled too many times. There's worse by far, but... I also sort of don't care though, the costume system is better than the outfit system, and I'm fine with throwing my crowns at costumes. The costumes have a variety of unique models, to create that satisfying visual distinction between different people running around.