Well, I'm one of the people that use [] for qw. I very seldomly use () as delimiters; parenthesis already have a couple of meanings, using them as delimiters as well doesn't contribute to code clearity in my book.

My favourite delimiters are:

Operator     Pref.     Other
             Delim.    Delims
q, qq, qx     {}       <>   //   !!
qw            []       //   {}   <>
s, m, qr      //       {}   <>   !!   
y, tr         //       []   {}   <>
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I never use '#' as a delimiter (althought it's popular with many people).

As you can see, all the delimiters I often use tend to be long, narrow, and mostly vertical.