What type Roof Vent is best to reduce ACU heat load?
I would suggest a solar powered vent that way when it is sunny or more heat load the solar powered vent(s) can do a better job at removing the excess heat.
the first house I added a fan I used a standard 120v  thermally activated fan it would kick in mid morning and cut out in the late evening it made a massive difference in that homes comfort but did cost a few dollars for the power.
the next house I used solar. The great thing about solar is I have the highest airflow in the early afternoon when it really needs it and it was still cooling until the evening.  I live right at the 45 parallel so your results may be different than mine But the solar fan was great really reduced the heat load in each house and became the first thing I have done to my houses Before the first summer. I have not lived in any of my last 3 homes long enough for the fan to fail or the solar cells but as with most motors greasing or oiling the bearings extends the life and the solar cells were rated at 20 years.
I have had really good luck with solar but Oregon rarely gets 100+Lots of hazy cloudy days so maybe my solar cells are lasting longer because of that reason. I do have to spray them off with water as the horses kick up dust and that slows the fan down. But that is the extent of my maintenance at my current home after 5-6 years.