I agree with Dave. The most important consideration is your trim. You only need to be able to ditch enough weight to become buoyant in an emergency, and that does not take much.
If I personally had to distribute 12 pounds, I would agree with the poster who would distribute 4 3-lb weights. But that's me.
You also have to deal with what is available for you when you dive.
When I dive with a 3mm suit, 8 pounds is about right for me usually. Not long ago, I was on a boat that offered only 4 pound weights. Two of them would have been fine, but they would have all been at my waist, ruining my trim. Just for a test, I put 8 pounds on my waist and 8 pounds in my shoulder pockets--double my normal weight. I had a great dive. I felt perfectly balanced and in control the entire time.
I am thus a great believer that trim is more important than the perfect weight, and I strongly suggest you mess around with different configurations until you find the one that works best for you and your body.