Fuel tank sending unit for 1966 Dart?

On first sentence, are you saying the 3/8 units are better?? Thanks for all the info!
If you're doing something like building a race car and need a larger sending unit, like a 3/8" or 1/2" one, then yes an aftermarket one would be better. Otherwise no, the OEM ones which are 5/16" are fine and don't have the numerous drawbacks I listed.