When I was an undergrad, there was a fairly substantial group of us in both Greek and Hebrew. When we talked about this question, we discovered that those of us who had preferred algebra in high school had had better luck with Greek, while those who preferred geometry had taken to Hebrew faster.
Now, granted, n= about 15 here, but it makes sense to me -- in Hebrew letters are dropping in and out, and the whole structure's built around 3-letter roots that morph and change in (fairly) predictable ways, while Greek is more rigidly mathematical in how words shift through the paradigm.