well if you are going for the horde theme then skaven or a goblin army would fit quite well. But mostly it depends on exactly what type of army you want to play.
Off of the top of my head these are how some of the armies are split. Some armies are in multiple spots since they can be set-up for different methods.
Magic oriented:
Vampire Counts
High Elves
Empire
Skaven
Lizardmen
Tomb Kings
Combat oriented:
Beasts of Chaos
Warriors of Chaos
Bretonnian
Dwarfs
Empire
Vampire Counts
Skaven
Orks and Goblins
Lizardmen
Tomb Kings
Shooting Oriented:
Wood Elves
High Elves
Empire
Skaven
Orcs and Goblins
Dark Elves
Dwarfs
And of course the amount split up.
Horde:
Skaven
Orcs and Goblins
Empire
Warriors of chaos
Lizardmen
Elite:
High Elves
Dwarfs
Dark Elves
Vampire Counts
Empire
Of course this is just the armies that I play or have played against and the way that they were set-up.
Off of the top of my head these are how some of the armies are split. Some armies are in multiple spots since they can be set-up for different methods.
Magic oriented:
Vampire Counts
High Elves
Empire
Skaven
Lizardmen
Tomb Kings
Combat oriented:
Beasts of Chaos
Warriors of Chaos
Bretonnian
Dwarfs
Empire
Vampire Counts
Skaven
Orks and Goblins
Lizardmen
Tomb Kings
Shooting Oriented:
Wood Elves
High Elves
Empire
Skaven
Orcs and Goblins
Dark Elves
Dwarfs
And of course the amount split up.
Horde:
Skaven
Orcs and Goblins
Empire
Warriors of chaos
Lizardmen
Elite:
High Elves
Dwarfs
Dark Elves
Vampire Counts
Empire
Of course this is just the armies that I play or have played against and the way that they were set-up.