I run each motor off of a separate tank. Reasoning is:
1. if I have a motor problem, I can switch tanks/motors to see if that is the issue,
2. I always add the same amount of fuel to both tanks. This keeps fresh fuel in both tanks, plus on long trip where we are completely refilling the tanks, I can tell if one motor is burning significantly more fuel than the other.
Did this same practice on my 272 Sailfish.
When I bought my 330 Express, the former owner ran both engines off one tank, never ever switched tanks, and I ended up with the aux tank full of bad fuel/water.
So no matter what you decide, be sure to switch the motors to the other tank every other trip in order to keep your fuel fresh.