I sweat a lot and the bulk of my riding is in hot weather that some won't even go outside to ride in. So airflow over aero will be for me. The Giro Aether seems to have plenty of airflow and was on my short list before choosing a Specialized S-Works Prevail II.

But if you already have a good helmet for general riding, you can certainly get the aero helmets like the serious TT guys use. Then when it's not sweltering outside you can see what it does for your times.

If you don't see much difference in your data, you can console yourself by remembering that cooler drier air is denser than hot moist air.