The previous good deal was 14 pieces for $34.99. Since there is an additional promotion going on, Sears jacked up the price of the 14 piece set to $39.99. However, for some really screwed-up logic, Sears did not jack up the price for the 16 piece set. So the 16 piece set is actually cheaper than the 14 piece set as of now. (38.99 vs. 39.99), which makes it a no-brainer. Relative to the 16 piece set, the 14 piece set is missing the stubby and extra long driver for Philips size 0. Not a big deal, but they surely won't hurt.
Money wise, you will get $20 back in points. But most likely, you will also get some coupons or surprise points. I have both, but they cannot be used together. So I choose a $10 off $20 surprise points. Since I can use the points meaningfully, the final cost is 38.99 - 20 - 10 = 8.99 plus additional tax. Shipping is free. 56 cents per screwdriver! It is pretty hard to beat!