...and my reticular implant says...
The first design is the best. I disagree with JD about pins versus fins. The "finnage" extends the effective surface area from the baseplate, which is why it works so well.
Now, it might be possible to use a different pin arrangement (i.e. spacing) to obtain similar results to the first one, but I believe that the first design will always outperform pin-style blocks.
Consider the WhiteWater, Cascade and the G5 blocks: the fins are continous throughout the core area. (not obvious on the Cascade/G5, but it's there).
More info here:
http://forums.procooling.com/vbb/showthread.php?t=6101 (where it all started).