How to improve the looks of a fraction?

We may notice that the numerator and denominator in the following fraction are not aligned. And, to me it does not look good.

How to align the numerator and denominator?

\documentclass{article}

\usepackage{amsmath,mathrsfs,xcolor,mathtools}

\begin{document}

$$\dfrac{1-k^{m+n+d}}{1-k}$$
\end{document}

The above yields:

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Not a real improvement, but here it is: \frac{1-k^{m+n+d}}{1-k^{\hphantom{m+n+d}}} – egreg Sep 25 '12 at 8:52
@student What is the easiest way to do that? – User 17670 Sep 25 '12 at 9:25
In my opinion, aligning them is not a good idea, since the terms are importantly different. As well, as @egreg points out, the "aligned" result is not much good nicer. You can maybe shift the denominator just slightly: \dfrac{1-k^{m+n+d}}{1-k\quad} But I'm not sure it looks nicer than the default one. – yo' Sep 25 '12 at 9:42
@tohecz I'd definitely use the default centering. – egreg Sep 25 '12 at 9:43

Here's a comparison of the proposed solutions; the name next to the fraction doesn't necessarily denote the suggestion author's preference.

\documentclass{article}
\usepackage{amsmath}
\usepackage{mathtools}
\begin{document}
\makebox[2in][l]{1. Original}$\dfrac{1-k^{m+n+d}}{1-k}$

\bigskip

\makebox[2in][l]{2. egreg}$\dfrac{1-k^{m+n+d}}{1-k^{\hphantom{m+n+d}}}$

\bigskip

\makebox[2in][l]{3. projetmbc}$\dfrac{1-k^S}{1-k}, \text{ with$S=m+n+d$}$

\bigskip

\makebox[2in][l]{4. Peter Grill}$\dfrac{1-k^{\mathrlap{m+n+d}}}{1-k}$

\end{document}