"The codex is an Alexandrian text-type manuscript written in the 4th century in uncial letters on parchment. Current scholarship considers the Codex Sinaiticus to be one of the best Greek texts of the New Testament, along with that of the Codex Vaticanus. Until the discovery by Constantin von Tischendorf of the Sinaiticus text, the Codex Vaticanus was unrivaled."
They do, however, closely resemble each other.
The presentation in the Codex Sinaiticus Site is extremely useful, giving the ability to pinpoint the exact word in the manuscript. (Since the manuscript is written in uncial, this has always been a daunting task.) My presentation from the Vaticanus/Sinaiticus Verse Selector at the center top link on the main page is more brute force for Vaticanus, which relies on some penciled-in verse notations. Where my link is superior is in the translation and its harmonization of the Four Gospels and also of Acts with Revelations. The Codex Sinaiticus Site translation was just cobbled together as a guide as there is current no translation that reflects its text or Codex Vaticanus. (This is an amazing fact that nullifies all interpretations that have been based on less perfect texts! The best translation today is Revised Standard Version (RSV) which is also linked in my Codex Vaticanus/ Sinaiticus verse selector.) In my link I used Young's Literal Translation (YLT), but it has been modified in some places and explained by the Pesher of Christ™.
For completeness I recommend accessing all of these from my Vaticanus/Sinaiticus Verse Selector at the center top link on the main page