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;
     },
 });

##</code><code>##

         Rate  Atr  Btr   Bs   As
Atr  696801/s   --  -2% -13% -45%
Btr  711990/s   2%   -- -11% -44%
Bs   800289/s  15%  12%   -- -37%
As  1260797/s  81%  77%  58%   --