We had a whole house fan and loved it.

The newer attic fans are solar powered and run during the day, while the whole house fans run at night when it cools down.

Even if they run at the same time, it's not a big deal since the whole house fan draws air from outside, through the house, into the attic, then out the soffets/vents back outside again; in other words, the whole house fan will perform the attic fan functions as well.

The only downside was heat from the attic radiating through the closed whole house fan vent during the day, but it wasn't as bad as I thought it would be when I bought the house (and I didn't have an attic fan).