Here you will find information about the different classes & specs available in TBC. Please be aware that as of now, classic TBC hasn't been officially announced, and everything here is speculative based on what most people expect blizzard to release if they release classic TBC.
This guide will help you determine what class & spec you want to play based on your playstyle. As you walk through this guide, everything will be ranked on a scale of 1-5 on Desirability and Skill Required across multiple aspects of the game, as well as Leveling Difficulty.
Just because something is rated a 1, doesn't mean it's bad (and when it is it should be apparent). For example, if you're just starting into MMOs (or are just a lazy player) and want an easy class to play, having something with a difficulty ranking of 1 will allow you to get used to the game mechanics without overloading yourself. When you're ready to hear about the different classes / specs of TBC, start by clicking the role you wish to learn more about to the left.