for 3D cells and a regulator, a Wizzard would be a good choice, It will keep the LED from beign overdriven from fresh new cells, and then after the cells drop lower it will boost the voltage so the LED stays bright at the same level until the batteries are dead. So it keeps it at a constant regulated current. The LED stays happy (no overdrive at first on fresh cells) and it stays even brightness.
A wizzard 700-1000ma would be a good choice for a LuxIII and 3D setup.
It's worth the price if you want the same brigthness the whole way through the batteries (it will suddenly dim down to a dimmer level letting you know it's out of regulation, and still give you useable light. it won't just shut off though when the batteies are used up.). It's aslo worth it if you don't want to stress the LED when you put in fresh batteries as the voltage can be as high as 1.6volts per cell fresh, and drive an led at 1.6-1.7 amps fresh...
With a good expensive high performance emitter, (UX1K) I'd go the regulator route. Then your light would be top of the line all around.
If cost is an issue, a cheaper LED and resistor would be the route to go.