My best experience has been with Italeri helicopters in 1/72 scale. I've built quite a few of them and they go together very well, with few fit problems. I like the detail they have as well. Italeri also has the largest selection of 1/72 scale helicopters to choose from, followed by Hasegawa.
Here are some examples of Italeri Helicopters in 1/72 scale that I've built, just so you know what kind of quality Italeri has. I apologize for any poor photos, I have a bad digicam:
My British AB 47 Gunship. Can be built as U.S or Italian as well:
This next one is kind of hard to see well, and I apologize, but this next pic is of my British AH 64 Apache. This was taken at my IPMS club meeting by someone else. This kit can be made either U.S. Army or Dutch as well:
This next one is one of my favorites. I was so glad when they finally released a kit of this, especially since it was in 1/72 scale! It is the Italian AH 129 Mangusta from the Italian Army:
This is one of the smallest helicopter kits I've ever built. It is only 3 1/2 inches long! It can be built either U.S or Italian Police as well:
And finally, the Army's rather futile attempt to make a gunship out of the venerable Chinook:
These are some of the examples that I have of Italeri helicopter kits in 1/72 scale. Most of my 47 Helicopters are from Italeri, while the rest are from Hasegawa, Revell/Germany, and a few cheapees from Starfix that took massive amounts of work before they looked good. But hey, they were only a buck .25 at the local closeout store! :-)
Hasegawa makes good helicopters too, and so does Revell/Germany. So, among those three, you'll find a great selection of 1/72 scale helicopters that are good builds.