There is never a reason to leave Emacs.

M-x eshell

M-x term

I wish. Every now and then I try and use emacs term. It is slow, doesn't handle screen resizes well, and God forbid you try and use tmux within emacs term. You'll be sorry.

I prefer M-x shell - simple bash syntax and full emacs editing capabilities. But it's also painfully slow. Typing ls -l in the wrong directory and I'm tempted to kill the buffer. On the other hand, this encourages me to use M-x dired which is way better anyway.

I know it's not the same, but you're supposed to use multi-term to manage multiple terminal buffers.

bash has emacs keybindings by default