TV definitely Oberyn. Like Daario, he has plenty of word of mouth. However, he basically beat the biggest, baddest guy in the Seven Kingdoms with contemptuous ease. Plus his reach and poison will be very difficult even for Daario to contend with, as being much smaller, the poison would affect him much faster. And even a small nick would be match ending in a short while(due to him dying, or it weakening him enough for Oberyn to press his advantage).
The one trump card Daario has is his dagger, but I think Oberyn is possibly fast enough to dodge it, or make sure it's not fatal.