@Anywhere is best suited to very low-touch integrations where the user will likely be utilizing a Twitter feature for a very short period of time on your site. It’s fallen a bit behind the times in that it doesn’t support such tasks as uploading media, automatic t.co URL wrapping, and so on. For many of the features @Anywhere provides, Twitter Web Intents, the Tweet Button, and the Follow Button provide more relevant experiences.
I would recommend using the REST API for any long-term integrations where a relationship with the Twitter user wants to be maintained for a significant period of time, or if you want to use advanced features of the API.