It probably does not matter much how you mount stuff. If you want maximum cooling for the CPU at the expense of other components, like your graphics card, then bringing fresh air from outside to the inside is better. You then have to balance the exhaust so that equal or more air will flow out. This can be difficult when you have a hard drive constellation that also needs cooling, along with the use of glass sides.
Spinning drives really don't like it when they are run at above 50C. The expected life decreases rapidly above this temperature. SSDs are not quite so temperature sensitive, and also generally create less heat due to lower power requirements.
If you exhaust air over the radiator, then you get a bit less CPU cooling, but things may be better for the hard drives and graphics card.
If the fans are high static pressure fans, then they will be more efficient in push rather than pull operation, but they will work either way. All-in-all we are talking about only a couple of degrees difference in the various temperature profiles. In some cases you don't have a lot of choice about where to mount the radiator and fans.