The tests by Soldsecure and CyclingPlus indicate they are equally strong against the sorts of tools crooks typically use.
I prefer the NY 3000, because it weighs "only" four pounds. The strongest chains, plus padlocks weigh considererably more.
I've noticed that a lot of messengers in Houston prefer chains. Messengers have to be fast to make any money, and don't have time to go hunting for a steel pole that is the correct size for a "U" lock. The chain locks enable them to lock up to light poles, telephone poles, trees...lots of locations that a "U" lock would not fit.
I don't mind looking around for suitable locking locations, so the "U" lock works fine for me. My everyday locks are mini U-locks from OnGuard and Kryptonite. Although they are mediocre on the "test" bench, mini locks work well on the street. They simply don't provide enough empty room to insert effective leverage and breaking tools, and (knock on wood) the use of power cutting tools is not a problem in my neighborhood.
The best locks are those with a "gold" rating at soldsecure.com. The "Magnum" chains and U-locks with "gold" ratings are sold in the USA under the OnGuard name. The best OnGuard locks are a bit heavier than the best Kryptonite locks, and generally did less well than Kryptonite locks in Cycling Plus tests using power cutting tools, but equally well against leverage type attacks.
I'm going to echo part of what alanbikehouston said and say that I perfer a chain for the reason that I can actually use it. In most Europen cities there is nothing small enough to lock your bike to with a mini U-lock. A chain gives one many more options of where you can leave your cycle.
Check out the dimentions of the mini U-lock that you are thinking of buying and make a cardboard mock up of it. Then go around to the area where you will be leaving your cycle. Are there secure places to lock up to? Grocery stores are a perticular problem.
Remember, many street signs are not secure as they pull out of the ground very easily or the signs can be removed very quickly, allowing a theif to slip the bike up and over.
I plan to leave it somewhere that has a 'bike storage' facility, so I assume the D lock will fit round, but I understand what you're saying. Unfortunately, I can't actually visit the location I plan to lock my bike at before actually moving there for good (couple of weeks).
Thanks for the replies, Mat