Samsung is the champion when it comes to Android devices, and it makes sense that they would have the latest version of Android in their smartphones and tablets. While Android N was announced two weeks ago at Google I/O, some Samsung users are still waiting on the arrival of Android M (otherwise known as Android 6.0 or Marshmallow). This is the latest news on Android M Version 6.0 Marshmallow and Android N Release Date for Samsung Galaxy S6, S6 Edge, S6 Edge +, Note 5, Note 4, and S5 on Verizon, AT&T, T-Mobile, US Cellular, and Sprint.
The current flagship phone the Samsung Galaxy S7 has Android 6.0 right out of the packaging, so that is pretty much taken care of. Also under the "taken care of" column should be the Samsung Galaxy S6. Gotta Be Mobile reports that Samsung started a Marshmallow Beta test in Korea and a few other regions, which allowed actual users to receive it early. It is similar to what Motorola has done, and Samsung kicked off the Galaxy S6 update in February.
So whatever your carrier that you have the S6 with, whether it is Verizon, AT&T, T-Mobile, US Cellular, or Sprint, you should have it. This goes for the S6 Edge as well, as well as the S6 Edge+ in some markets.
As for the flagship from two years ago with the Galaxy S5, the update started sometime at the end of May. There are reports that Sprint, Verizon, and AT&T have the upgrade, so it might be available for you, depending on your region. Anything earlier than that with the Galaxy S4 and S3 probably won't be getting it, period.
As far as the Galaxy Note 5, the most recent phablet from the company, is concerned, it looks like it has its upgrade as well. There has been conflicting reports with the aforementioned Gotta Be Mobile article saying that only AT&T doesn't have it, while Tech Radar states that only T-Mobile has it.
As far as other and older versions of phablets go, it looks like the Galaxy Note Edge has been getting Android 6.0.1 on factory unlocked versions of the handset in Europe. There are reports that the Galaxy Note 4 is getting its update as well.
Users of "newer" Samsung devices are encouraged to check your "Settings" and "System Updates" to see if Marshmallow is ready to download. This upgrade might not be ready depending on your U.S. carrier, as it has been shown that certain carriers receive the Android upgrade before others, with no real pattern.
When it comes to Android N, it is going to be coming to Samsung products, and it probably will come up to everything up to the S6 and above. It probably won't be coming out until around the holidays, and that is being pretty optimistic, as generally Samsung receives their upgrades at the beginning of the year following an announcement of the new Version of Android in the previous year.