#2 Stay in NXT to reclaim his title
This option is probably the most expected direction as the main rosters don't require call-ups at the moment. Moreover, there's still a chance that Gargano gets a shot to reclaim his title before SummerSlam.
Gargano's chase for the title was a dream run. Whether it involved Andrade, Aleister Black, Tommaso Ciampa, or Adam Cole, each rivalry gave a top quality match. Hence, after Johnny won the title after so much effort, he won't let it go away without one last try.
It's not necessary to win the title back, a rematch between the two would finally put Gargano's story to end.
#1 Conquer 205 Live
Although 205 Live is a part of the main roster, it's highly separated and distinct from its counterparts. Instead of being the third brand, it has become a stepping stone for the cruiserweights to get to RAW or SmackDown.
While he might get lost in the shuffle on RAW or SmackDown, he would be the biggest superstar on the purple brand. He could conquer and carry the brand on his shoulders. It would be mutually beneficial for both the superstar and the brand.