More importantly, the NEMA 5-15p is internally grounded. That's what the 3rd pin is for. It's not strictly necessary, and some Darwin-award candidates have taken it upon themselves to remove the ground conductor, but needless to say, it's a bad idea. This is the one you'll want to use, especially for an outdoor application like a bug zapper.
Additionally, you have 2 different types of the "standard" 2-pronged plugs in the US. The first is unpolarized. Both blades are of equal width and the plug can be inserted in either direction. The second is polarized, which has a slightly thicker blade for the neutral conductor.