Empire is a good starter army, rather flexible army They were my first army.
As cool as Dwarfs can be, I'd steer you more towards Lizards. Lizards also have some mobility Dwarfs don't... heavy hitters, and the same armor (With the option of spears). Lizards are also a little more fighty.
So Empire or Lizards. Lizards might perform a bit better, but are less flexible.
Chaos Dwarfs: Wins/Loss/Draw 20/13/7
Wastelanders (Chaos Space Marines): Wins/Loss/Draw 8/3/5