We use the ready made formula cartons. They're expensive but there is no way I'm going to wait for 30 mins for the water to cool down!
When ds was younger we had the perfect prep which is amazing. Alternatively you can have half cooked boiled water, mix the powder with the other half water fresh from kettle then shake all up together. Result is lukewarm feed, all sterile water and the powder is mixed with boiling so it kills any bacteria in the milk powder. It essentially works the same way as the perfect prep machine