Meh, they both work fine. That said, I like to have a numerical debug level -- categories are too complicated, and on-or-off is too coarse -- and to write debugging statements like this:

dprint 1, "this is debugging"
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Then you can implement dprint as e.g.

sub dprint {
    my $level = shift;
    return unless $DEBUG >= $level;
    my ($file, $line) = (caller)[1,2];
    print STDERR "$file:$line: @_\n";
}
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