"Heatsinks seem to have a similar situation, where you have square and rectangular heatsinks, and then you have your circular or oval ones. It seems like the majority have gone the way of the rectangle, making them bulky and cumbersome, but with performance that was better than their circular counterparts. Interestingly enough, the circular designs are stilling being produced, yet now, some are outperforming the previously unstoppable rectangular ones.
The Thermaltake MaxOrb EX is a horizontal flow, circular heatsink designed for high air flow. The Thermaltake MaxOrb EX features six copper heat pipes for improved heat exchange performance. The circular design allows for a lower profile than most stacked heatsinks, but is optimized for maximum air flow and cooling characteristics."