Welcome to the forum, @maynard!
I recommend both, each for different applications.
Aquaseal is best for installing valves, making permanent repairs, and gluing fabric together in places that can’t be heat-sealed. (Aquaseal cures with exposure to air, so when gluing two things together, apply Aquaseal to both surfaces and let them sit for at least 30 minutes before pressing them together, otherwise it will take a very long time to cure fully.)
Seam Grip is thinner and can be applied with the included brushes along the inside of seams so that even if your heat seals aren’t perfectly airtight, your tubes will not leak air. (Aquaseal can be used for the same purpose, but it won’t cover as much area.) Seam Grip can also be used to patch very small holes.
