Answers

HardiePlank is a fiber-cement siding, whereas SmartSide is an engineered wood product.  Fiber cement products do not rot as easily as wood products and most builders will recommend fiber cement over wood for that reason.  If you choose either of these products, you will need to be dilligent about maintaining them (painting, checking for rot, etc.).  Your other major option would be vinyl siding, which does not have the aesthetic appeal of wood or fiber cement, but is much easier to maintain.