As a dinghy racer, blue water cruiser, and flashaholic, I have some opinions on the subject!
First, you really need to know what the intended use is. Lake sailing or offshore sailing? Certainly being offshore raises the bar a bit.
For use while sailing at night, you need more than one light:
1. Low output light for routine tasks. This is extremely important since on a sailboat at night, light levels are low and you need to try to preserve night vision. I wear a CMG Ultra-G on a neck lanyard for general duty on the boat at night. A Dorcy 1AAA might be good too: if you drop it overboard, you are out 7 bucks. A little keychain red led light would have a role here too.
2. Handy throw oriented light used mostly for checking the rigging up high or the set of the sails. Though a variable output light would be ideal here, a Streamlight 4AA ProPolymer Luxeon might be better. If it does roll overboard, no great financial loss. It almost floats with lithium AA cells. Add a keychain float to the lanyard and I think you would be good.
3. Bright, powerful incandescent light for those unplanned night time anchorage approaches. Incandescent to cut through all the moisture in the air, and high power since on the water distances can be quite long. A Thor or equivalent would be great. My Mag85 does fairly well here too.
4. PFD light - traditionally a strobe of some sort, but it can be hard for searchers to judge distance with a strobe, or pick it out from the clutter of shore lights. I would supplement it with something small, bright, and water resistant. An Eternalight loaded with Lithiums since it floats, can give some eye-catching LED patterns, and doesn't take up much pocket space.