I'm under mounting a sink to a slab of granite and there many different brands of epoxy. Is one better for this type of job?
Absolutely not. Epoxies are formulated for different cure times, cure temperatures, bonding to different materials, performance in various extreme environments, etc. That said, amongst the various hardware store 5 minute general purpose epoxies, I doubt there is a lot of difference between brands. I know nothing of the specifics for this application, I would expect there is a specific adhesive to use and recommended by the sink manufacturer. If not, I would check with the stone supplier for recommendations.