You should go for what you like! If you prefer to be Tauren, go for it! You can even adjust their size with baby spices, pygmy oil and stuff like that. You can be a gnome-sized Tauren if you like ^.^
That said, if you want the better races for PvE/PvP as you said yourself, Gnimo is right.
Orcs are superior because they get more expertise when wielding Axes, have an attack power-boosting racial, and are passively more resistant to stun effects. This can be further enhanced through talents.
Humans have increased expertise with swords , increased stealth detection, and their racial active can break them free of slows and trapping effects.
These things are huge both in PvE and in PvP, making Orcs and Humans the most optimal race choice, compared to the others.