I have the Fox Sharx, the Fox Sonik Blast and the Storm. The following review is subjective, as I have only blown each whistle ONCE without ear protection.

The Sharx and Sonik Blast are about identical loudness. The Sonik Blast has a smaller footprint. However, the Sharx has a friendlier shape and is a work of art to me. These whistles have approximately 2 volumes: silent and screeching loud.

The Storm is the loudest and seems to allow more control over loudness. However, the Storm is huge and bigger than it looks in Internet pics. The Storm has a pea that provides an oscillation sound, which is absent in the Fox whistles. The pea may be a concern if you are in frigid conditions because the pea might freeze. I don't know because I don't take my Storm into freezing conditions. Actually, the Storm is so big that I find myself not taking the Storm anywhere.

In my everyday carry bag is a Sharx. Around my neck when I'm snowboarding is a Sharx. Around my neck when I'm biking is a Sharx.