Table of Contents Services (such as those listed below) vary in the journals they include. All of them provide ToC/alerts for journals from a large number of publishers. As a result, it may take a smidge longer for them to send out alerts but they are quicker to set up and easier to maintain.
In comparison, publisher alerts (see the separate tab on the left) are usually faster than other alert services because publisher websites are the first place information is made available. This information is then sent to other vendors. The drawback to publisher alerts is that they usually cover a fairly small number of journals while Table of Contents Services cover several thousand journals.