I'm hard-to-fit in clothing, as I am a bigger guy who is just under average height.  I've found Columbia Ultimate Roc pants to be perfect for me, as they are true-to-size.  They are durable (I've run them through the washer and dryer dozens of times - almost no fraying), stain-resistant, roomy, and made of "breathable" fabric.  I just ordered two more pairs to go with the four I already own.

Be sure to buy the "Ultimate Roc" pants, as they are a slightly different cut and fabric from Columbia's ordinary "Roc" pants.