Subjective opinion, but it depends on the overall look trying to achieve. I have put in many over the years, and 95% of clients chose white porcelain.

I have the Kohler Whitehaven cast iron short apron front sink. It can be installed on a standard sink base. I was also looking at the Kohler Hawthorne because I initially wanted two equal bowls. However, it was much more expensive then the Whitehaven and I would need to get a new sink base cabinet or really work hard to try to retrofit my present cabinet - needing to get new doors.

I decided against fireclay because I am a klutz.

I did not write this - it is from one of my favorite blogs - but it solidified the feelings I already had:

http://victoriaelizabethbarnes.com/apron-front-farmhouse-sink-options-decided-against-fireclay/