Laurence,
The ones that I have always liked are Warn W520's. They are SS, with 2-axis mounting brackets [so they stay put where you aim them], and single wire hookup through the stem [assuming a good ground]. I used to run two in front above the winch as an alternate/supplement to headlights, and one as a back-up light on the left side of the rollbar of the grey truck. They are sitting in a box in the garage waiting to be put on the Heep one of these days.
From an optical perspective, a flood lens / reflector is better than a spot or driving, as you won't be going fast in reverse. Also, the smaller lens [5" vs. 6"] for a given wattage lamp means less distance, and hence greater intensity over a relatively short distance.
For a back-up light application, mount a single light on the driver's side; that way, when you look over your right shoulder, you get the light, but no glare in your face like if you had put one on the passenger's side [or a pair]. Aim it to the center, use the optional 100W bulb, and put a dedicated fused & switched circuit using 14-12 gauge wire.
That's my .03.