Well it depends, if you have free electricity it's better to get more less efficient miners because you can get that for very cheap, and the time to paying them off will be short.

But if you have to pay for it, then yeah. Efficiency is king. But you probably don't want to go for the most efficient still. Maybe you can get a 15J/Th for 20 $/Th but a 13.5 J/Th would cost you 30 $/Th.

I went for an S21 pro and hosted it in Dubai for 7.5 $/KWh. Let's see how it goes😎