Much depends on how you plan to kill the rabbits.
If you are working lurchers, you need a lamp with a cowl so that you illuminate the rabbit but not yourself or too much of the surrounding landscape. For shooting, it's not so important to have a cowl as the lamp is either gun-mounted, or someone else is operating it, allowing the shooter to position him/herself correctly so as to remain hidden.
The 'Gamekeeper and Countryman, paper has a full page ad in most publications. 'Shooting Times' is another. Or here
http://www.wighillparkguns.co.uk/products/products_category.asp?cat=141 Some people favour red filters and claim they decrease the potential for spooking rabbits, but they do decrease the range of the beam to an extent.
I like the variable power option as there are often occasions when less light is a good idea, such as when moving between areas, crossing fences, checking weapons for faults or dogs for injuries, etc., saving much battery power, thus extending operating time.
If you are planning to lamp with lurchers, you will need a lamp and portable power source. If you plan to shoot from a vehicle you will be able to use a hand-held plugged into the cig lighter, or a roof-mounted to the same source, or wired directly to the battery. The latter are operated from the interior of the vehicle.