A recent evaluation by Bit9 is noted below and the actual list can be found in links below

The 12 Most Vulnerable Smartphones

QUOTE: How vulnerable is your smartphone to malware attacks? Android is by far the most targeted mobile operating system, but some popular Android phones made by Samsung, HTC, and Motorola, fare a lot worse than others. Bit9, an enterprise-oriented security vendor, ranked the 12 most vulnerable cell phones (the “dirty dozen”) based on how dated its software is out of the box. Android fragmentation is well documented, but your average cell phone user probably doesn’t care if he or she’s on Android 2.3 or Android 2.3.7. Functionally, the versions are similar.