Different uniforms connote different things. Having a few standby outfits and rotating based on duty and scenario, and they bring different things to the table.
Putting themselves on display for me is always important to remind them of their primary purpose; thigh-highs with heels or boots, chokers & collars, maybe some opera gloves, but always clothed exposure via cut-outs or sheer/see-through. Open-cup bras, showgirl skirts, bodysuits with access windows, etc.
Elaborate "take me now Master" lingerie is always welcome, but using that as base criteria you can combine that with the mood you're going for and their current duty rotation. Naked apron if they're cooking, slutty maid if they're cleaning, reverse bunny if you're entertaining guests, and so on.
Really the matching/coordinating is doing a lot of work all on its own. The fact they are not only there to serve your will but are surrendering their sense of self to the collective of your harem/squad/what-have-you. Reinforces the hierarchy of command and the promise of more, more, more. Bonus points for acting as one, too; lineups, salutes, marching, speaking in unison or one after the other...
Sorry what was the question?