3DXtreme.net has posted a comparison review on the DangerDen Maze 4, AquaXtreme MP-1 and Swiftech MCW60 Performance Comparison. Here is a quote:

We came into this comparison with the possible expectation of obtaining results that distanced the waterblocks from each other a little more than what we actually obtained. For those who like to squeeze the most performance out of their system possible then we would probably recommend the AquaXtreme MP-1 as the best waterblock. It provided the lowest delta T and while it provided the most restriction it performed as advertised by the manufacturer even with low flow. As for the regular users who have ventured to watercooling in an attempt get the most cooling possible but aren't worried about small differences in delta T, then any one of these waterblocks is recommended. The prices for these blocks is about the same and their quality is equal. AquaXtreme, DangerDen and Swiftech all have winning GPU waterblocks here.

In related news, PCApex have a new review up on a CPU waterblock from Swiftech named the Apogee.