So to provide context, I often dual wield in spinning choreography. I am pretty decent at it and have a fair number of tutorials that have been well received. That said, if I were to duel, I would opt for a single saber to get an advantage based on my style and ability. This is for a few reasons.
1. Economy of motion. when we are talking about unskilled users, sure dual sabers is an a great advantage. This is because the more sabers you have and the more you move them, the more visual noise you create. If your opponent is not comfortable with attacking, this will throw them off. The same goes for spinning and any other flash. You won't see this though with professional duelists. A professional duelist does not care what you do with the saber if it is not a threat. They will defend when needed and look for an opening. Pro sparring matches are a lot less exciting than fights in the movies for this reason. Skilled combatants practice an economy of motion unless they are messing with you. The shortest distance is a straight line, and once it forms, you have a problem if you can't interrupt it. This is not to say that dual wield cannot have this economy of motion, it is just not as well suited to it. More blades to move means more movement means more openings if you are not careful.
2. Reach. If you dual wield two weapons you will be awkward unless you are using shorter weapons. longer weapons will swing wide and leave you wide open. If you use shorter weapons like they do in doce pares, you get a big advantage to speed assuming you can close. If you watch a match of escrima against kendo, quite often the escrima person puts this to good advantage. If you watch a match of escrima against foil or epee though, the reach often trumps this and the escrima combatant often gets stabbed as he tries to close distance. Movie saber is very martial arts based, but practical saber dueling when it comes right down to it, tends to be more like the European schools. For this reason, I prefer the advantage of reach.
Now for the record, in the right hands, dual wield is a great style. Like all styles, it has advantages and drawbacks. If you are quick and agile, go for it. If you can dodge a strike with minimal parrying, you can close and do real damage. I know that I am more calculating than kinetic, so I would go with a single wield if I wanted to have a better chance to win.