Actually, you may be able to have both, in one.
I recently installed fan rated @ 1540 cfm in S attic gable. About 15"
diam. If I leave door (which is sealed) to attic closed, fan does
decent job drawing from N gable end. Fan has make-on-rise adjustable
temp-switch. Temp rise on floor below is greatly reduced; ditto thermal
stress on lumber & roofing above.
If I leave door to attic open, and open distant windows below, fan
ventilates whole house very nicely. For fall, and beyond, I'll have to
wire in some sort of timer-switch in parallel w/t-stat. Or, a second
temp switch with a lower set-point, switched in parallel with first.
(Or even a timer in series w/ second temp-switch for whole-house, in
parallel with attic-only temp-switch.)
Some folks I've seen in the past use 3' or larger diameter fans sucking
from house up through attic. And may even need them. In my case, such
a fan would suck in the screens or lift the roof-deck, or both.