I tend to have any individual capable of worshipping any of the gods as their specific god and also many of the gods as they go about their day. A merchant may like Waukeen most as the god of merchants and commerce, but when getting on a ship might donate to Umberlee to not destroy his goods, or Talos for good weather.
Towns and villages tend to have a favored god that most everyone uses as the main god since that's how it always been. Same with the other races, but I tend to have the specific gods in areas dominated by other races.
I also look at the gods as part of the same thing or concept. The god of healing might show himself to humans as one thing and orcs as another thing, but still be the same god, just using different faces. Although my games do not get into this that much and it has mot come up in play. May this is a bit like the Star Trek movie with the god at the end of the galaxy, and he kept changing faces.