Smart url is popular tracking service right now but there are quite a few others. Like Kenny said more results depends on the site and ad copy, stale emails from the site and stale splash pages don't get the response fresh eye grabbing capture page gets. You are marketing to people who are burnt out on the hard sell. Matthew Graves will tell you these first contact mails on safelists are to build a list; a tribe that know,like, and trust you, then you sell to your list.