I'm going to argue that it depends on what you mean by "important." What controversy is currently most important to fight about? What controversy will we look back on this time and realize was a major social or political focus? What controversy will we still be fighting over in 10 or 40 years?
History has shown that the most "important" controversies to fight, were the ones where human life was in danger. Here I think of our involvement in WW1&2. On the other hand, there are those that are still arguing the US should have never involved itself in the conflicts in the Middle East. Perhaps, instead, the abortion debate will one day be looked back on as a worthy cause.
I also wonder what medical controversies (today) will very possibly be the solutions to medical questions and potential cures. Stem-cell research is highly controversial, as is genetic engeneering. But what if scientists one day discover, through these pursuits, the cure for cancer, AIDS, or one of the many genetic birth defects? Then, we'd be looking back and saying they were important medical controversies.