Looking at what we know of the new rules I think you are going to really be nerfed if you take a single class Paladin, Ranger, Monk or Fighter compared to what you can do with a dip.
On a Paladin I think you are going to always want 1 Warlock level.
On a Fighter you are going to want 1 Warlock level to let you attack with Charisma or 1 Monk level to make bonus action unarmed strikes.
On a Monk you are going to want a level of Fighter or Ranger for Nick.
On a Ranger you are going to want 1 Monk level for bonus action unarmed strikes.
Multiclassing has always provided an edge, but now the boons you get with a one level dip make the difference between a dipped and non-dipped character pretty big. I don't see single class martials being competitive with these dips at most levels.
On a Paladin I think you are going to always want 1 Warlock level.
On a Fighter you are going to want 1 Warlock level to let you attack with Charisma or 1 Monk level to make bonus action unarmed strikes.
On a Monk you are going to want a level of Fighter or Ranger for Nick.
On a Ranger you are going to want 1 Monk level for bonus action unarmed strikes.
Multiclassing has always provided an edge, but now the boons you get with a one level dip make the difference between a dipped and non-dipped character pretty big. I don't see single class martials being competitive with these dips at most levels.