Macron and Mélenchon are both unacceptable.
Why is Melenchon unacceptable?
I always liked Melenchon more than Hamon, to be honest.
Why?
Now that the presidential election is over, I will answer. It is because both Melenchon and Hamon run as anti-neoliberal candidates, but only Melenchon has the backbone to call Merkel's bluff on the EU. Running a non-neoliberal economy policy in the Eurozone is fundamentally contradictory and unsustainable. We saw this during the Euro crisis 2009-12. As soon as any nation strays too far from orthodoxy, the bond markets will slap you back. Thus, Hamon would have been doomed to failure and unpopularity. Melenchon might have as well, but he would at least have had a chance. Hamon would have had no chance.