It's almost 100% personal preference. If I had to redo my exhaust, I wouldn't do anything different. Some say you loose low-end torque with duals, which is true, but it's so microscopic you wouldn't notice it unless you owned a dyno.
First, are you going to run cats? It's much cheaper to go the single 3" with a cat, since obviously two cats will cost twice as much.
Second, what do you want it to sound like? Quiet? Loud? Obnoxious? You'll want to keep the cats if you want to tone it down a bit. Mine has no cats and it's loud but it's exactly how I wanted it. Again, personal preference.
Third, if none of the shops around there will do duals (which I think is really odd) then is it even an option?