The hamon is a complex deal. When you say "better" , do you mean more contrasty or more activity? I mean, lots of steels (even 5160 and other low alloy steels...) will make a hamon and the level of contrast (how bold it is when polished) can be quite high. What we are seeing in the case of differentially hardened low alloy is just the crystaline difference between hard and soft steel. The edge is (to some degree) Martensite. The body will remain "something else" and polish differently and have a different lustre. Almost any plain or low alloy steel can make a good, contrasty hamon.
But activity is a different deal. Like the swords you see where the hamon forms clouds and swirls and the habuchi (that little line of bright white crystals that delineates soft and hard steel areas...) is wide or has swirls and cool stuff in it and we see areas of dark and light within the actual hamon itself. Activity is exploiting the different areas of hardenability and walking a very close line between hardening and not hardening.
Japanese use steel that is in the .6 to .7 carbon range but there are layers of all kinds of stuff in there...pattern welded steel that is low in hardenability makes some really cool patterns.
In monosteel I find that 1050 and the lower carbon/higher Manganese steels can make a wider and fluffier habuchi and get activity that is very close to the Japanese blades. The higher carbon steels do a great job as well but crack more easily and tend to have a thinner habuchi. The higher carbon steels that lack Manganese still develop wild hamon with a lot of activity but they need to have their hardenability lowered by thermal cycling.
For examples of the differences, do some web research on Bob Engnaths katana blades made of 1050, look at Rick Barretts katana for higher carbon done in oil, and look at Howard Clarks stuff to see what a .86 percent carbon steel can do when modified and heat treated by a master.
http://www.summerchild.com/be_consignkatana.htm
http://www.barrettcustomknives.com/
http://www.mvforge.com/index.html
Needless to say, this whole idea of which steel is best for making hamon is a huge concept and is very complex. Differential heat treat to make a visually appealing hardening line and still maintain a good performing blade will take a lifetime to master. Lots of steel will work just fine if the craftsman spends the time to get familiar with the quirks of the steel and learns to exploit it.
My opinion is that there is no "one best" steel for makiing hamon as there is no one "best" way to do anything in the world of cutlery. It's all research and then doing it in the shop, over and over again, until you learn the secrets and get a handle on the practical, real life aspects of what you are trying to accomplish.
If I was going to start making blades with the only criteria being a cool hamon with a minimum amount of cracking and issues I'd start with 1050 and go from there.
Brian
(thanks for the steel Don.....I want more 
)
