Air conditioners

What is the best most economical air conditioner to buy for  3 x 4.5 x 3.5  bedroom &  4 x 6 x 3.5 lounge /kitchen. Both areas will also have ceiling fans and be completely air tight.
We are buying 2 aircons, so should the bedroom one be smaller as the space is smaller?
Also what's the difference between inverted and non inverted and roughly costs to run?


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