I always declare lexicals at the point of first assignment, if possible.

The issue almost becomes irrelevant if one keeps lexical scopes short. Of course, this is often not practical. If I do find myself with a block several pages long, I'll revert to style #1 for variables that are in fact used "throughout" that scope, even if first assignment isn't at the top of the scope. But if, in a pages-long block, there is a valid need for name re-use but not value longevity, I will often introduce bare blocks just for the purpose of constraining the scope of distinct variables, rather than recycle a single variable. E.g.

{ # long block begin
   .
   .
   {
      my $name = 'foo';
      .
      .
   }
   .
   .
   {
      my $name = 'bar';
      .
      .
   }
   .
   .
}
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Oftentimes, if the net effect of a section of code is to produce a value, a do block is useful for introducing an "artificial" scope. E.g. instead of a plain bare block like this,

  my @lines;
  {
    my $fh = new IO::File "< $infile";
    @lines = <$fh>;
  }
  for ( @lines ) { ...
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I might use a do block, like this, which obviates an auxiliary variable:

  for ( do { my $fh = new IO::File "< $infile"; <$fh> } ) { ...
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(Note that lexical scopes are also useful for constraining the effects of local operators.)