I switched because most of my team uses brew, but I was happy with macports, it has a sane UI and I liked the way build options could be specified (i.e. "+python +png")

The only problem I had was that some stuff requiring compilation _outside_ of macports have builds that won't work naturally (e.g. phashion gem).

This is usually solveable and rare, but annoying. OTOH I've seen similar issues with brew too (i.e. need to change openssl from system version to compiled version and recompile stuff)