I don't like polls too much:
The helicopter would have to perform ground support, tank elimination, etc.
All the types you listed can do that and most countries don't have large tank formations anymore so taking out tanks isn't as important as once was. Overall performance, cost, weapons suite, counter measures, maintenance hours, hot and cold flying, data links, targeting radar, etc, mean much more then destroying tanks.
Types you listed:
Bell AH-1Z HueyCobra
AH-64D Longbow Apache
Both saw action
Boeing RAH-66 Comanche - I believe the project was canceled and was never produced.
Eurocopter Tiger - will see action soon
Agusta A 129 Mangusta - I don't think its been in combat but there is a chance it has, its been out for a while
Denel AH-2 Rooivalk - No sales yet and don't think South Africa use it in combat yet,
Kamov Ka-50 Hokum
Kamov Ka-52 Alligator - Either the Ka-52 or the Mi-28N according to some Russian web sites had four or five flights in the Chechen's conflict. For me difficult to prove (helicopter flights) and the Chechen's conflict in general little information was released about the air war part of the fighting. If you ever find any please post it or PM me, thanks.
As you can see asking which is the best when only a handful has been in combat is difficult. You left out the Mi-28N type which actually won the Russian choice for attack helicopter to replace the Mi-25 series. But like most things Russian almost eight years and just this year a engine was chosen so going into full production is another matter.