My top UI 3 gripes would probably be:

1. Retainers: If it's too much work or not possible to simplify/unify the Retainer UI then at an absolute bare minimum allow me to MUTE the retainers. When then talk to me (when the "you called master" or whatever it says bubble appears), it is one more step of MANY i have to click through. Plus, I have to CLICK or hit the Confirm key, I can't just pound the ESC key until I back out to the level I want.

2. All of the Inventory screens (inventory, saddlebag, armoury, retainers, etc) need to be more easily sortable, by all of the various stats (clvl, ilvl, condition, spiritbond, etc), in the UI itself. Yea there's the /itemsort command that can be macro'd, and I have a few of those (sort armoury by spiritbond, armoury by materia). But I can't have macros for every combination of list/stat.

3. A way to more easily consolidate inventory between myself and retainers (and other places too i guess). As it is now I spend way too much time running /isearch and "Search for Item" commands trying to stack all of one type of item in one place (like making sure all of my Steel Ingots are on Retainer #1 instead of spread out all over the place).