GHS Brite Flats (Alloy 52 half-rounds) are what used to come on Stingrays from the factory. Their tonal character is more flatwound than roundwound.
GHS Pressurewounds (Alloy 52 rollerwound) are more roundwound in their tonal character than the Brite Flats.
Based on what I've read, the Rotosound Solo Bass 55, being stainless steel, are brighter than the GHS PWs and not as smooth in surface texture.
By the way, a lot of Stingray players seem to like the Ernie Ball Cobalt Flats as an alternative to the Brite Flats. They're flats that are designed to sound like rounds.