Let me preface my recommendations by saying that you should definitely ask some local divers what they use. They'll know exactly what cuts through the local murk.
If you were diving in a tropical locale, you could get away with a smaller light. Since you're probably diving in a local quarry, you should err on the side of too-much-light. In San Diego waters, I have had good luck with the
Princeton Tec Shockwave eLED (about $100, 8-C batteries). I wouldn't go with anything "smaller." They're a good value for the amount of light that they emit. LED lights are whiter than the yellowish halogen lights. Furthermore, lights that use regular halogen bulbs are much more fragile than their LED counterparts. I have dive buddies who are quite happy with the UK Light Cannon, which throws out a stonger yellower light than the Princeton Tec Shockwave eLED. Before making your purchase, you should know that the Light Cannon bulbs are quite expensive to replace (almost $100) and can be damaged easily if you were to drop the light onto pavement from about waist height. (Don't ask how I know.)
If I had to make my purchase nowadays, I'd get the 4-C LED light called the
Miniwave LED. I'd also get some good quality rechargeable C batteries like
these in addition to a
solid charger. That setup should keep you going for several years.
I'm sure others will chime in with their preferences. UK is pretty good with their customer service, although recently one of my dive buddies had to wait 4 months for a wonky light to be replaced under warranty with them. Apparently, the replacement bulbs were on backorder for quite some time. Go figure.
I haven't had the need to test Princeton Tec's customer service. Their lights have performed admirably for me over the past 5 years. YMMV.
Don't forget to get a smaller backup light. I use the Princeton Tec40 (4AA) as my backup. It's inexpensive (<$20), small, and reliable.
Good luck with your night dives. They're my favorite!