#1: Readability is better for the map version, in my opinion, though the 'x' operator version isn't bad, and is measurably faster in the uncommon case where such considerations actually matter. ;)

use Benchmark qw( cmpthese );

@array = ( 'aaa' .. 'zzz' );

cmpthese ( -3, {
  mapped => q{my %hash = map{$_=>0} @array},
  opped  => q{my %hash; @hash{@array} = (0) x @array},
} );

__END__
         Rate mapped  opped
mapped 65.9/s     --   -45%
opped   120/s    82%     --
[download]

But except for the odd case of doing such a transform inside of a tight loop, the benchmark is probably totally inconsequential when weighed against the legibility issues.

#2: I prefer the ternary operator. Everyone knows what is happening here. The 'x' operator version is a nifty contortion. And it would be silly to bother thinking in terms of processing time in such a trivial snippet; I suspect the result would be within the margin of error.

So for me, map, and ternary. I would love to favor the slice approach, but it takes a little more cognition to mentally evaluate.