When it comes to link shorteners, and I have used a few, I find them not to be very effective. Anyone who sees your ad knows instinctively that you are an affiliate.
If you really want your web address to stand out, buy a domain name. They can be very cheap and you get to choose whatever name you like, as long as it hasn't already been taken.
When you buy your own .com or .org or others, your ad will look much more professional. You can also have it so that it forwards to your affiliate link so no-one knows that you are just an affiliate for the product or service.
There are many domain registrars but probably the best two well known ones are goaddy.com and hostgator.com. Type in the domain name you want into other registrars to find out the best price.