`brew install sl` if you want it on OS X.
I've never found a port I thought should have been in MacPorts not being there, `sudo port -v install [package]` always seems to work, and dependencies are automagically followed.
Looking at the website, it seems the general "improvement" is that you can edit formulas before you install; but that's exactly why I use MacPorts! I don't want to know how to install all these things, that abstraction is something I prefer. If you don't intend to do this, is Homebrew really any different?
You can edit the MacPorts portfiles too, if you want to:
sudo port edit <portname>
Which means that if install Git, that's all I get. With Macports, I'll also be installing duplicate versions of at least curl, openssh, and rsync, as per http://help.github.com/mac-git-installation/
Homebrew tries to take the high ground here, but it's just naivety. They'll wind up installing "duplicate" versions of software too -- in fact, they already are doing so. The short-cycle of Leopard -> Snow Leopard won't be happening again soon, and the only alternative to adding "duplicate" software to your dependency tree is letting software go stale (for example: python 2.7 vs SL's 2.6.1).
It's easy to say that the 10 years of knowledge that both MacPorts and Fink have about the platform is "stupid" when you haven't had the experience of maintaining a working packaging/port system through a few OS X release cycles, and aren't familiar with the problem space or Apple's policies.