Good question:
For me, macports is the one.
Why? I'll bypass a lot of stuff and cut right to the chase:
The party is over with regard to malware, trojans and the like. Paging through the last security update, there were some vulns that were from the summer although the cure only came last week. Redownload the developer tools, recompile your macports install, and you have a functioning toolchain that is not dependent on Cupertino, since the Dev Tools from your install disk will serve. Who uses an old version of Openssh? Now it does take some care and feeding, like running port selfupdate every day, and the big tip is to check
port variants
so if you have a python dependency, you can run
port install python +no_tkinter
and avoid the agonizingly long Tk install, which would be most unwelcome on a Quartz architecture anyway.
With this, you can freely run software update and not have your stuff break, since it does not depend on anything but the compiler from apple. I've used it for a long time, and although I tried some others, namely Homebrew, I think that depending on apples versions means inheriting their security flaws. Remember that PDF hole on the iphone? I deploy on Linux anyway, so for me, macports tree is the 'office' and my budding MacOS dev career is 'home'
Just an opinion, but the separate tree for all the code is a big plus for me.
You might take a look at VirtualBox which includes a GNU GPL version as well. It offers limited/experimental capabilities to run virtualized OS X VMs, but I think Apple generally forbids virtualizing OS X via their licensing/usage terms.
Best Answer
You basically have three options for Virtualization on Mac OS X:
Any of these will allow you to run a variety of OSs under OS X without resorting to bootcamp or repartitioning.
The last two are not free, but -depending upon your needs- vastly superior in terms of features to VirtualBox. I have the three. I have used the three extensively. In its current versions, Parallels is ahead of VMware. But this changes very often with new versions. Virtual Box is ok but slower (to virtualize) and has way less features.
VMware is very stable. It never crashed in more than three years of daily usage. Parallels does perform certain tasks faster than VMware, but will occasionally crash the VM. (It happened about 5 times in a two year period).
In the end, either will work if you don’t need anything fancy.