to be more precise, since hot air rises, front should always be intake. if a fan it placed on the back at the top, it should be exhale. all top fans should be exhale, as for the side ones, it depends on where the side fans are placed, as well as how much air can get past your gpu. if your gpu is so large that almost no air can pass through, have the side on exhale, if not, then the side is usually an intake fan if its placed near the bottom.
in the end the fans air circulation should either be
L shaped with air coming < and exhaling ^
as well as Z-ish shaped where air is coming < and exiting the top at < direction
in perspective that you are looking at the case on the side that opens.