Chromium-Browser would be my recommendation but like what T6 posted, we have Firefox, Opera, Konqueror, Rekonq, Epiphany, Seamonkey, Dillo, Jumanji, Midori, Qupzilla, the dead Flock, etc. that are alternatives. I am sure that with enough prodding, users can make them just as fast (if not even faster), secured and streamlined as what others are using.
I am quite happy with my use of chromium-browser but I'm sure it isn't for everyone. But since we are on the topic of Iron, it is probably the closest to an alternative.