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Based on this article the MBP has has a higher pixel density

At 217 pixels per inch, the pixel density is just a smidge lower than that of Apple's MacBook Pro with Retina Display, though it's safe to assume most users would keep the iMac screen further away than a laptop.
 
Does it have better or lower pixel density?

According to isthisretina.com , the retina iMac has a PPI of 217.57, the 15" rMBP is 220.53 PPI and the 13" rMBP is 226.98 PPI.

To be honest I can't tell the difference between any of them unless I pixel hunt them.
 
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