Weak group. Vote goes to Mongols.
Indonesia is bland (for good reason) but fulfills an important role.
Mexico is completely boring because Leoreth refuses to give them a meaningful UP, but again fulfills an important role.
Mongols are impossible to balance (especially on 3000BC starts and on Normal speed) but it's reasonably well-designed now with the new Keshik unit. Of course, its role is perhaps the most important among all civs. And finally it's not boring. So it edges its way out of this group of dark horses and qualifiers.