I'm looking into further optimizing my debian systems, but I am still fairly new. I was wondering, what is the difference between apt-src and apt-build? Will either build packages for you? Which one is easier to use?

Thanks!

It depends on what you want to do; apt-build is just a set of scripts to apt so that you don't have to do things like the patching and specifying lines like "apt-get source build-dep somepackage" + dpkg-buildpackage.

apt-src downloads source but in such a way that you can use it to update source as you hack away at it (or so the package seems to claim).

Why do you want to build packages? The only packages I can think of which may benefit from a build are the kernel and libc. The only other times I actually build software (but usually don't package as a deb file) are when I need some code which hasn't made it into the Debian archives yet or I'm hacking at my own code. If you want to build packages just for the experience, go for it - but building everything from scratch as Gentoo can doesn't really get you any significant gains.