JDUB800 As a licensed user of both, I've found Fusion to be by far the most robust and stable of the two.
As someone who updates firmware on various home devices via PC USB, Fusion has performed excellently on every occasion - Alas, the first time I tried it with Parallels, it blue screened, bricking the device - leaving me at the mercy of the device's warranty. I've never used it since. Thankfully the device was replaced and since, I've used Fusion to do this with no problems! :)
(Version 1.1.2)