I've had good results with Net::FTP::Robust; however, most of the ftp servers that I use are set up to retrieve or accept files only. You'll see "I can only retrieve regular files" in this script:

#!/usr/bin/perl

use strict;
use warnings;
use Net::FTP::Robust;
use Log::Report;

use constant HOST => 'ftp.perl.org';
use constant DIR  => '/pub/CPAN';
use constant FILE => 'README';

my $ftp = Net::FTP->new(HOST, Debug => 1, Passive => 1) 
          or die "Couldn't connect: $@\n";
$ftp->login('anonymous');
$ftp->cwd(DIR);
$ftp->get(DIR);

try { "error" };
if($@) { '../CPAN' }

$ftp->quit;
[download]

Update: You can dramatically speed up file transfer by using Net::FTP::Throttle
Try this:

#!/usr/bin/perl

use strict;
use warnings;
use Net::FTP::Robust;
use Net::FTP::Throttle;
use Log::Report;

use constant HOST => 'ftp.perl.org';
use constant DIR  => '/pub/CPAN';
use constant FILE => 'README';

my $ftp = Net::FTP->new(HOST, Debug => 1, Passive => 1, 
         MegabitsPerSecond => 2) or die "Couldn't connect: $@\n";
$ftp->login('anonymous');
$ftp->cwd(DIR);
$ftp->get(FILE);

try { "error" };
if($@) { '../CPAN' }

$ftp->quit;
[download]