Griezmann has been thriving in Atletico because he was the main man forward. Also, Most of Atletico's Penalties were also taken by him which helped raise his goal tally. Imagine going to Barcelona well almost all Pens are given to Messi
I think PSG would be a good place for him now that Cavani is slowly fading off and Neymar is always on clutches.
Manchester United? Very very bad idea for now
If Griezmann leaves Atleti there is no way Man Utd is a realistic team for him to join. They are crap, no CL football & no hope. It’s going to take years for them to compete for the big trophies.