You can't get kernel-specific things like strace, but they do have just about everything else. The big sell for me was being able to install the GNU versions of everything.
Macports keeps everything in /opt, so you also never have to worry about it clobbering anything that MacOS expects to work in a certain way.
edit: some background on Macports vs Homebrew - it's basically a vi/emacs kind of a thing. Homebrew utilizes the MacOS system stuff a fair amount, and installs everything to /usr/local. Macports tries to keep everything fully separate, and installs into /opt.
My personal experiences with Homebrew weren't great, but others will probably have the opposite opinion.