I'm one of the el-get devs. I'd say the main advantage of el-get for the gp is that just installing it doesn't modify your emacs config in any way. In contrast to something like the ESK, it is
not an opinionated set of defaults to help new users get started. It is literally nothing but a system for installing and initializing elisp code. Many of the recipes provide some initialization code to set up the code being installed, but you can completely replace that code with your own if you don't like it (or you can decide not to use the provided recipes at all and just write all your own).
It's definitely a more hands-on, low-level tool than ESK, designed for those who want the fine-grained control of a manually-built emacs config without all the manual labor of git-cloning (or hg cloning, or downloading and untarring, or cvs checkout-ing) the several dozen elisp repos that your config uses. It definitely matches my use case, which is why I kept submitting so many pull requests that the original author finally just gave me a commit bit :).
Note that I'm not saying that el-get is in any way better than ESK (I've actually contributed to ESK as well even though I don't personally use it, since ESK uses my ido-ubiquitous library). El-get is just designed for a different purpose.