#!/usr/bin/perl -wT
    use strict;
    my @lol = ([1,2,3],
               [1,2,3,4,5],
               [1,2,3,4,5,6,7,8],
               [1,2,3,4],
               [1,2,3,4,5,6],
              );

    my $index = 0;

    $index = $#{$lol[$index]} < $#{$lol[$_]} ? $_ : $index for 0 .. $#
+lol;

    print "\$aoa[$index] has the most elements\n";

    =OUTPUT
    $aoa[2] has the most elements
[download]

And just for the fun of it, a bit faster if you have a couple hundred thousand lists in the list at the cost of extra clutter :-) :

    my ($index,$len) = (0,0);

    $index = $len < $#{$lol[$_]} ? do { $len = $#{$lol[$_]}; $_ } : $i
+ndex for 0 .. $#lol;
[download]

I'm still trying to figure out what blakem was thinking btw..