Basically which of the Marvel licenses owned by other studios would you like returned to Marvel (MCU) most?
X-Men
Spider-Man
Fantastic 4
For me it would be Fantastic 4 to have Dr. Doom and the Silver Surfer back for Avengers 3 to face off against Thanos. It would also bring in Galactus for another big threat or an unwilling ally to take on Thanos and the Infinity Gauntlet. Also the Fantastic 4 working with the Avengers and on their own done by Marvel could be great.
(Note: I think these are the only licenses not held by Marvel but maybe wrong.
X-Men
Spider-Man
Fantastic 4
For me it would be Fantastic 4 to have Dr. Doom and the Silver Surfer back for Avengers 3 to face off against Thanos. It would also bring in Galactus for another big threat or an unwilling ally to take on Thanos and the Infinity Gauntlet. Also the Fantastic 4 working with the Avengers and on their own done by Marvel could be great.
(Note: I think these are the only licenses not held by Marvel but maybe wrong.