In the case of hardware store bits, I believe the TiN drill bits are just an excuse to not use the correct alloy steel or give it the proper heat treatment. If you can find High Speed Steel bits from a specialtly manufacturer like the Triumph Twist Drill Company or Greenfield Tap and Die company, they will last much longer than any coated hardware store bits. The coated specialty bits are even better still, but way out of anybody's price range. Cobalt drill bits are the hardest and most expensive and because it's not just a coating, the hardware store cobalt bits are usually of good quality. Cobalt bits will typically be a more of a tan color than the gold of TiN.