OK looking at guns and accessories

If I want to apply Base's and Clear's AND had to pick either a 1.3 or 1.4 to do both which would be better choice and why?

Assuming 1.3 better for clears (a bit thinner) and 1.4 better for bases (a bit thicker) is this a correct assumption?

Best bet is to go with the recommended tip size in the product tech sheet for the product you are applying.

If I had to make a broad generalization, a 1.4 tip seems to be a common choice. A larger tip will (obviously) allow more material per second to pass through the nozzle than a smaller tip will, given the same product being sprayed. This also speaks to other variables, like how fast the painter is comfortable moving the gun, and how well the product atomizes given the tip size.

Some guns come with multiple tips so you can use the one best suited for the job

Chris is right,,,go with the 1.4.

I agree with Chris ... look to the charts put out by the paint companies. They test most of the major spray guns with their paints under common conditions, and recommend a needle/tip based on HVLP or compliant cap and the specific paint properties.
Here's a link to some of the paint company charts:

http://www.autorefinishdevilbiss.com/spray-gun-setup.aspx