There are two choices you have for your home:

RAFTER MOUNTED SYSTEMS or CEILING MOUNTED SYSTEMS.

Once you make a choice between those, you then have other choices to make:

The most important choice is whether to install insulated ceiling openings.

See the INSULATED SYSTEMS That  MEET IECM2012 SPECS

Next, how many speeds are best for your needs?

SPEEDS – 1, 2, 3, 4, 6,  OR INFINITE?

Air flow – you need to decide how many CFM you want. The more the better.

CFM – HOW MUCH DO YOU NEED?

Attic ventilation – what goes up must go out

VENTS IN YOUR ATTIC – HOW MANY DO YOU NEED?

Efficiency – This varies greatly between suppliers. Do you want to pay more for better efficiency?

EFFICIENCY – WHAT DOES IT GET YOU?

Here are some more details:

SOUND LEVEL – WHAT ARE SONES AND dBA?

CALIFORNIA ENERGY COMMISSION LISTING – WHAT DOES IT MEAN?

SILVER FOIL ATTIC RADIANT BARRIER – HOW GOOD IS IT?

INSTALLATION – CAN YOU DO IT YOURSELF?

ACCESS TO YOUR ATTIC – YOU NEED TO KNOW EXACTLY

JOIST SPACING – DO YOU KNOW YOURS?