IS - Generally speaking, if you are going to use the construction "one of (something)", it is going to be in the singular because it is ONE. Take a look at these examples: One of my favorite heroes is Abraham Lincoln (obviously talking about one person here) One of my favorite types of shoes is Nike's (still one, because it is *one type*) Now if you use a slightly different construction that pluralizes the subject, it will be different: A few of my friends ARE going to the movie (because there's more than one friend going) THESE ARE a few of my favorite things (because you will list more than one thing) Hope that helps! - R

Definitely is.

Eine meiner größten Interessen ist wandern. The same in English = One of my biggest interests is hiking.