The 2 has basically the same mechanics where MyLikes & Ad.ly will provide you the sponsored links, which you will tweet to your twitter timeline. Then, you will earn from every click that you get from the sponsored tweets you posted.
The only difference is how you can choose what sponsored tweets you can endorse. In Mylikes.com, they will present to you a list of their tweet campaigns (advertisements) with their corresponding click rate. Then, you can simply select from the list which ads you want to tweet. But please note that some ad campaign may only pay to US accounts.
I kinda prefer the style of Mylikes because you have more options on what ad campaign you can do. Though, I’m not really a big fan of twitter advertising for the reason that I don’t want to spam my friends. Of course, unless it is something I really really believe in.
As to how good the payments are, I can always say that you cannot really depend much on it.