use Benchmark qw( cmpthese );

 cmpthese( @ARGV ? $ARGV[0] : -3, {
     Atr => sub {
         $string = "blah+blah+blah";
         $string =~ tr/+/ /;
     },
     As => sub {
         $string =~ "blah+blah+blah";
         $string =~ s/\+/ /g;
     },
     Btr => sub {
         $string = "blah+blah+blah";
         $string =~ tr/+/ /;
     },
     Bs => sub {
         $string =~ "blah+blah+blah";
         $string =~ s/\+/ /g;
     },
 });