Good question.
In this application, you're bonding aluminum (service port connector) and what I'd assume to be brass (the R-134a adapter). Both bonding products are a form of epoxy. The biggest difference is that the JB Weld has the suspended steel/iron particles in the solution.
Personally, I think that either would work sufficiently for your purposes, so go with whatever you currently have readily available to you.
Best luck![]()