Hive are the greatest threat, directly at least. Hostile Fallen are almost extinct, hostile Cabal are dwindling in number...well outside Shadow Legion cloning, Scorn have no leadership to rally them and make more, and that leaves the Vex. The Vex do things on their own time and schedule. The Hive are the most numerous and most directly aggressive hostile force out there.

I personally think vex or cabal are the worst seasonal enemies

which are just hive