Most players use their outfit slots to display outfits for different situations. One slot dedicated to casual attire, one to a battle outfit and some extra’s for cold weather, a nice dress or other fancy stuff. I have only four outfit slots activated at the moment. I really don’t need more than that right now as I change outfits at the vault all the time anyway.
I do have one outfit slot dedicated to battle. I like to keep a good view of what is going on so I usually don’t use cloaks during battle as they tend to get in the way. I either don’t equip them or switch them off. Since I view my character from the back all the time I do like it when the back part of the chest piece is decorated. My favourite battle outfit (and sort of my signature outfit) for my minstrel is the Everstout. It’s a rare drop from Barad Gularan, but I’ve been told it drops in Carn Dum as well. The matching leggings come from the same place. Both pieces are not bind on acquire, so you may find them on the Auction House sometimes. The same design might be available as a regular yellow world drop under a different name as well.
When looking for rare items on the Auction House, look for any armour that is “of might”, “of vigour”, “of fate” etc. They will usually be level 40+. There are lots of cosmetically interesting yellow items dropping in Carn Dum, Barad Gularan and in the Moria instances as well. Everybody always passes on those as players consider them “trash”, but they are treasures to a cosmetics collector like me and make doing those instances really worth while.