Correct the size of < > in math mode?

I am using \left< and \right> to indicate the average in an equation. Unfortunately it looks quite strange in the following example, as the automatic size estimation is different for both sides of the equation. Is there any way to fix this, so that it looks "correct"?

\documentclass{standalone}

\begin{document}

$\left< \Delta \eta \right>^2 \ll \left< \eta^2 \right>$

\end{document}


At the moment the output is as follows with clearly visible difference in size of the parentheses.

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you can also use \langle and \rangle. –  percusse Oct 30 '12 at 14:43

Like this?

Code

\documentclass[border=2pt]{standalone}

\begin{document}

$\left< \Delta \eta\vphantom{^2} \right>^2 \ll \left< \eta^2 \right>$

\end{document}


Or like that?

Code

\documentclass[border=2pt]{standalone}

\begin{document}

$\left< \Delta \eta \right>^2 \ll \left< \eta\smash{^2} \right>$

\end{document}


Or with fixed-size delimeters

Code A

\documentclass[border=2pt]{standalone}

\begin{document}

$\bigl< \Delta \eta \bigr>^2 \ll \bigl< \eta^2 \bigr>$

\end{document}


Code B

\documentclass[border=2pt]{standalone}

\begin{document}

$\langle \Delta \eta \rangle^2 \ll \langle \eta^2 \rangle$

\end{document}


Output

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Wow, thank you for the instant answer and complete overview. –  Alexander Oct 30 '12 at 14:49
I'd vote for the last method. –  egreg Oct 30 '12 at 21:08