I mostly build 1/72, so there may be some differences for the larger scales. As always your particular interests may also result in some variation. Helicopters are far less popular with the manufacturers so the options are not like other aircraft, you frequently have to take what you can get.
Italeri and Revell of Germany seem to offer the most kits, many reboxed from the other. Italeri also picked up a lot of the older Esci kits. Overall these two are probably the most reliably good kits although they are not without issues.
Academy, Fujimi and Hasegawa have a few helicopters most are good kits. The Hasegawa and Fujimi Huey's are not generally considered as good as the Italeri ones.
Hobbyboss is a fairly recent addition. Their Soviet helicopters have been well received, but most of their US helos have had issues. Their recent Seahawks seem to be an improvement over their earlier attempts.
Zvesda is one of the few options for regular production injection molded Soviet helicopters.
You may find some helicopter kits from Tamiya, but these are actually reboxed Italeri kits.