Which would use more power?

First of all, I'm NOT a pro HVAC (Heating, Ventilation and Air Conditioning) guy, but I work side-by-side with them all the time. Go ahead and laugh, but I've learned more about HVAC while eating lunch with these great guys/gals than you'd believe. They have some pretty good opinions on this one, and when I read your question, I heard them all telling me what to tell you (do you hear voices to??).

Smaller AC units, evenly distributed throughout the home are MUCH better than a large unit trying to do the job by itself. While the larger unit cools like mad, it can't possibly de-humidify that kind of cubic footage.

Dehumidifying is KEY to effective/efficient air conditioning.

Smaller units sharing the work-load consume a lot less power when not forced to run at maximum output 100% of the time, as compared to a large unit working it's tail off.

I'd also LOVE to hear some PROFESSIONAL opinions about whether I'm correct or incorrect (Thanx in advance).

I had what sounds like a very similar situation. I had one small AC cooling my living room hall and kitchen with the AC in the living room. My kitchen wasn't really getting cool. So what did was I got a larger one and put it in the living room and put a fan in hall facing the kitchen and now the whole areas cool.

Adding another AC wil definitely raise your bill where a fan wont nearly as much.

I think you'd actually be better off in the long run to have central air installed and get rid of all the small units. You'd probably use less electricity and have more even distribution of both heat and cool. Really, if you can get away with one window A/C that's probably better, but when you're talking about having 3 units to cool your home, you may as well go central.

Window units are designed to condition the air in a specific space….. according to how they are sized.

Since you are running window units I would purchase two smaller ones sized for the bedrooms …..and close the doors. Use the bigger one for the kitchen & living room.