The NXT Tag Team Championships are currently being held by Roderick Strong & Kyle O'Reilly of the Undisputed ERA.
The Undisputed Era has successfully defeated the likes of SAnitY, the Authors of Pain, Moustache Mountain, & Oney Lorcan & Danny Burch. However, they certainly won't be NXT Tag Team Champions forever.
#5: The Forgotten Sons
The 3-man stable of Wesley Blake, Steve Cutler, & Jaxson Ryker recently made their NXT debut by defeating the Street Profits. This team (Wesley Blake & Steve Cutler in particular) needs more time to develop on NXT.
The Forgotten Sons will probably spend another 2 years in NXT at least, so it is definitely possible that they will hold the NXT Tag Team Titles at some point in their NXT career. However, it is unlikely that they will have a long reign and will probably put over a team of faces such as the Street Profits.
#4: The Street Profits
The Street Profits made their NXT debut last year. They have managed to consistently improve their in-ring skills (especially Montez Ford) and are extremely charismatic.
They will probably win the NXT Tag Team Titles at some point before they are called up to the main roster (this will happen at one point next year or early 2020 probably). The Street Profits will then have a decent reign before being defeated by a tag team that is new to NXT.
#3: Oney Lorcan & Danny Burch
Oney Lorcan suffered an orbital bone injury at NXT Takeover: Chicago 2 during a match with Undisputed Era. Oney Lorcan was only recently cleared to return to in-ring action.
He made his return on last week's episode of NXT alongside his tag team partner Danny Burch. Now that they are back in NXT, it is safe to assume that they will begin right where they left off by challenging for the NXT Tag Team Titles. They will probably win the titles at some point next year (if they don't get called up to the main roster first).
#2: The Mighty
The Mighty recently changed their name from TM61 to the Mighty when they turned heel. The Mighty are one of WWE's most reliable tag teams in the ring.
This year, they've had excellent matches with the likes of Heavy Machinery, the Street Profits, & the Authors of Pain. Once the Undisputed ERA inevitably makes their way to the main roster, the Mighty will carry NXT's Tag Team Divisions as the champions before putting over Oney Lorcan & Danny Burch.
#1: The War Raiders
The War Raiders were signed by WWE earlier this year. They debuted on the episode of NXT after NXT Takeover: New Orleans.
They have run through every single team that has been put in their way. The War Raiders are currently in a feud with Undisputed ERA.
Both teams will probably be involved in the War Games Match at NXT Takeover: War Games 2 event in November.
They will then win the NXT Tag Team Titles at some point in between November & January from the Undisputed ERA before they will then lose to the Mighty at some point in the spring.