All of those have their strengths and weaknesses, but my first reaction is to pick the nature pair, because I appreciate their great speed & initiative. Plus, the sprites' no retaliation and wolves' double attack abilities are great.
Others I like: Dwarf and Halfling. I like the halflings not because they are an outstanding level 1 shooter, but because they usually have precision readily available to them via the mage controlling them. The dwarves serve as the halflings' bodyguards.
![smile_teeth :D](/forums/images/smilies/smile_teeth.gif)
Crossbowman & Squire: Same as above, except the crossbowmen need no precision to shoot without penalty.
Rogues (but not Orcs): for their ability to snatch resources and treasures at the very beginning of the game, which gives a great advantage to Chaos.