Good summation by batsbrew. For me, the two most-crucial MMultiAnalyzer features are normalization and the loudness histogram. SPAN+ has the more pleasant UI, especially if you're already a longtime SPAN user. But the lack of normalization makes it more difficult to compare two spectral signatures, when you don't really care about absolute levels.

I have been using MMA for most of this year now and it is awesome. It is very easy to setup so that you can see different track spectrums on one screen. The discounted price makes this a no brainer IMO.

batsbrew
Also cool is the "Deharmonize" mode, which allows you to get rid of harmonics and focus on the fundamental frequencies of your sources. 
 

 
 
Thanks bats! I didn't know that about MMA. I'll have to check it out.