CyanogenMod is what Android should be
Recently while I had some free time I decided to give Jelly Bean a try by installing CM10 on both my Verizon Galaxy Nexus(newly bought after frustration with Droid Bionic) and my Transformer Prime. After doing this I realized that almost everything about the way CyanogenMod works was better, except for installing it in the first place.
1. Fast Updates and Wide support
Pretty much any device with an unlocked bootloader that was released in the last two years is supported by CM and gets updates constantly. If your device isn't supported by CM, chances are there is an unofficial port somewhere to try out.
2. Real Open Source
Some open source proponents have criticized Android for calling itself open source, but only dumping the code after it is finished. On the other hand CyanogenMod is fully developed in the open, like Linux and most Linux distributions. This speeds up the development process by letting just about anyone fix bugs, as well as taking pressure off the people in charge of the software.
3. Nightlies /Release Candidates
One thing that is odd to me about Android is that it is one of the only major Operating Systems that doesn't let you try out beta software. I'm not too familiar with the matter but on iOS I believe you can install iOS 6 beta before it has even been released, whereas with Android you have to wait for both Google to finish it and for the Manufacturer to port it to your device. With CyanogenMod, you can choose to jump ahead to unfinished software and risk the bugs for whatever feature you just can't wait for(though CM can't start until Google releases it).
4. Consistent UI
CyanogenMod for the most part sticks to the stock Android UI with a few minor improvements, which is what a skin really should be. It also is pretty much the same on whatever device you use it on, which is more than you can say about android itself. With it's open nature, CM more easily allows you to change that UI if you want to, with either the theme chooser or just by changing the custom launcher. You could also go even further and use the base code in order to make a completely different UI which is what MIUI does, basing its code off of CM instead of Android itself.