Everyone has their opinion as to which is better and why. However, there is no reason to ever run double opt-in...in my opinion. There is no reason why you can't send your own confirmation email and then move those that click (confirm) to a separate campaign for those that confirmed. With many ESPs having automation features, you can move a user based on clicking a link. If you can't you could create custom script that collects the email and moves the user or at worst, manually do it. Technically, you don't even have to send a confirmation email. You could send a message with a link that should be clicked on. Link for you bribe. You could also confirm based on opening instead of click. If you want to be more lenient. Lastly, if you are proving a bribe, tell the user on your squeeze page that it will be sent to the email they enter. So they know entering in a fake one isn't going to work. By doing the above, you can can build a list of both and test and see if you are leaving money on the table using double opt-in. Also, if someone doesn't confirm using whatever method you choose, you can resend the message. Just my 2 cents.