What is best attic fan to install?

They are a gimmick. They can’t pull enough cooler air from outside to make a difference. They pretty much just spin already hot air around. They don’t ventilate or cool an attic anymore than a cheaper ridge vent or standard box vents. Try a Cobra: brand ridge vent instead. I work on houses for a living and power vents do not perform and are not worth the money.

If you have adequate insulation in your ceiling as well as around any ductwork running through your attic, attic fans are not going to make a huge difference. Attics usually have passive vents that allow some air movement, but if you have substantial heat build-up and inadequate insulation, you might want to consider the ridge vent that @buster recommended or a non-powered wind turbine that you frequently see spinning on roofs. The down-side is the installation would require you to make penetrations of your roof, which will require proper flashing to avoid leaks, or the turbine causing the roof to lift around it. If you believe your insulation is inadequate and heat build up in the attic is affecting your ability to cool the living space (or, heat it in the winter) or if you go into your attic space regularly for some reason, you might consider powered exhaust fans (manual or thermostat controlled), but these may require that your passive vents be enlarged to allow adequate air in take to compensate for the exhaust air volume. You might contact your utility company (gas and/or electric). They may offer programs where an energy consultant will come to your home at no cost to you, evaluate your situation and make recommendations based on energy cost savings. They may even offer rebates for your installation of approved energy saving hardware. I’ll see if I can find you a link that might describe better your attic fan alternatives. See ya…wtf (my initials)
PS: Welcome to fluther

Here is a link to a site that appears to address attic exhaust options (I did not read it so don’t know if it is a good source, but you might give it a look). Again, welcome to fluther and see you around….wtf

We have a whole house fan- with fans in the upstairs hall and bedrooms that vent out the attic. They work brilliantly- extremely efficient at cooling the house down once it is cooler outside than in.