If your hair is less than shoulder-length and thick, a mixed-bristle brush of intermediate size will meet your needs. The Junior or Handy Bristle & Nylon will serve nicely. If you think you might one day grow your hair longer, get the Junior.
I've also included the Pocket Bristle & Nylon here. Though it could serve as an all-round brush, unless portability is important, we think you will be happier in the long run with at least a Handy-size brush, both for its larger head and comfort in the hand. Remember, you may well have this brush for 20 years or more.
If you haven't yet had a look at our full Brush Guide, we recommend doing so.