Great question. 
For me, so far it’s been Guatemala 🇬🇹 
Their fan base showed up in Jamaica. 
Their fans showed up in Austin. 
They took down Jamaica. And gave Panama a run for their money. If they can get into the knockout round, that’s a game nobody wants. 
If they somehow face the US, I fear there may be more Guatemalan jerseys than American jerseys. 
This team has their country behind it right now. They may be the only country who can make such a statement in Concacaf.