Which exhaust direction is better for a CPU cooler?

It really doesn't make that much of a difference really, but technically you'll get the best temps by going for a method not listed in your question.

What you would do is switch your rear fan so it intakes instead of exhausts and then having your HSF (heatsink & fan) intake air from the rear fan so that the air that is going through the heatsink is as cool as possible. This way it isn't being affected by your other components inside your case and will give you the best possible temps.

For this method though I would recommend buying a 120mm fan filter though for the rear 120mm or else you'll be blowing dust into your heatsink which over time will degrade performance. This is assuming you have a case with dust filters, or else it really doesn't matter at that point. lol.

If your 5.25" bays are mesh and not solid this method will be even better, as some will exhaust out that way and some will go out the top fan.

i would orient it front to back because of the back fan.. you will also be able to cool your ram that way and it looks better anyways :P

the "heat rises" thing does not really apply here but the graphics card would heat up the are at the front of the cooler if mounted vertically

the best orientation is a front to back orientation with lots of cool air coming in at the front and all the hot air being exhausted out the back of the case

in case you purchase a retail field CPU, it comes with a heatsink fan. in case you purchase an o.e.m processor, then you actually really get the CPU no longer a heatsink fan... extremely the production facility heatsinks are plenty for regularly occurring builds. receive a loose software referred to as SPEEDFAN and save a watch on your CPU temps once you get it outfitted and also you could continuously purchase an o.e.m later down the line. something below 50C is perfect below load. Get yoruself some artic silver 5 and note to the CPU and sparkling off all that production facility gunk that they note to the heatsink with alcohol and cotton swabs. All you want is a imagine layer on the CPU die smoothed out with a razor blade or mastercard, then note your heatsink...

Basically, just consider the overall air flow. Most common is front to back, where fans on the front blow in, and fans on the back blow out. Set other internal fans to follow that flow where possible. Otherwise, set any internal fans to blow any heat up and away from the mobo (CPU excepted, those usually blow down onto CPU)

As long as the flow is consistent in direction, you will have good air flow, which provides the most cooling overall. A top fan on the case is best, if you have one. Check the PSU fan, which way it blows. Try to balance the number of fans in and out so they are somewhat equal (so if PSU fan blows in, add extra fan on back blowing out). If PSU fan blows out the back, that counts as one "out the back" fan.

If adding that top fan, count that as on "out" fan, and add another "in" fan at the front or side (if case has side opening.

My system has one top fan, one back fan and PSU fan (out back), two front fans (in), plus open vent on side (no fan) allowing that extra air flow into the case...

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the direction does not effect cpu speed