Huge difference.
Both are relatively harmless unless you mess with them or step on a stingray. They burrow into the sand to catch small fish and crustaceans.
AFAIK, Mantas are free swimming open mouth feeders.
I saw a guy step on a stingray once and it stung him in the ankle. A grown man crying in agony!..............
When wading in bays in Texas it is wise to do the “stingray shuffle” and slide your feet along with out picking them up. Nudge a stingray with your foot and it will scurry away. Step on one and you will wind up in the ER.