There are a few catches with MacPorts, though:
1) Installing and updating ports usually requires compilation. There generally aren't ready-to-download binary packages. For a single package, this may not be a big deal, unless it drags in a bunch of other packages that also have to be compiled.
2) If one upgrades OS X, the MacPorts maintainers recommend deleting and reinstalling MacPorts for the new version of OS X. I'm not sure this is always necessary, but I've preferred not to risk it.
3) A given version of MacPorts targets certain OS X versions, and there's a lag time between when the latest release of OS X comes out and when a version of MacPorts comes out that targets that release.
There's also Fink, which shares problem #3 with MacPorts. It's supposed to have binary packages available, but when I tried it recently, that didn't work out, and it acted much like MacPorts, that is, downloading source and compiling it.