OS X comes with a built-in terminal (that's actually pretty good). There's no reason for a beginner to reach for any third-party terminal software.
Yes beginner should start with plain old bash IMO.
A terminal emulator is not a shell. Using bash has nothing to do with the decision whether you use the OS X Terminal or some third party terminal emulator.
Besides iTerm2 maybe. Default config is very similar to the built-in OS X terminal.
I would not recommend iTerm2 to a beginner. The iTerm developers believe in the kitchen sink approach to preferences, which is not very beginner-friendly. And there's not much reason to use iTerm2 in general anyway now that Terminal.app has mouse support, I'm only aware of a few relatively esoteric features that iTerm2 has that Terminal doesn't (support for colors outside of the 256-color palette, and built-in support for showing tmux panes as iTerm window splits).
That's why I said that the default config is fine for beginners. Don't even need to open the preferences window.
pretty sure that iTerm2 for a beginner is pretty much identical to Terminal. At that stage don't know enough to leverage it's fancy capabilities so they don't get in the way and confuse you. When you're ready for them, they're there for you. In Terminal you have something that looks and works almost identical but when you want more you can't have it.
Personally, on OSX I'd go with iTerm2 any time of the day.