I would go with the 2005 myself but it is really up to you to decide which body style and size you want. The NHW11 (2001-2003) is a compact 4 door sedan with a trunk while the NHW20 (2004-2009) is a mid size 5 door hatchback.
Quoting another answerer:
"one has all the parts and pieces of a regular car to wear out and/or go wrong PLUS all the additional Hybrid gear to think about."
Wrong, The Prius has no starter, no alternator, no clutch/torque converter, no step gear transmission with clutch packs or synchros to wear out, no shifting other than the parking pawl, no timing belt, and no spark plug wires as it is igniter-on-plug. The engine is always spun up to at least 1000 RPM before combustion begins, the electric motor provides most of the motive power while the engine is cold, it runs at lower cruising RPM on the highway than a "normal" 4 cylinder thanks to the CVT-like PSD, and the North American version of the NHW20 has a dewar flask (thermos) that holds hot coolant to help preheat the engine during a cold start.
The PSD also means the engine never sees sudden load or RPM changes. When you press the accelerator farther down the engine RPM just ramps up instead of lugging more and more then downshifting.
