Android updates are consistent, but they are not consistently on time. When a new version comes out, the devices running even the second-to-the-last model are often slow to receive their updates. Such is the case with the HTC series with models like the One M8 and M9, not to mention the LG Series with the G4, G3, and even the G2. This is the latest on the Android Lollipop 5.1.1 and Marshmallow 6.0 updteas for the HTC One M9 and M8, as well as the LG G4, G3, and G2.
The HTC One M9 and HTC One M8
One thing that is for sure, it is expected that Android M will be coming to the HTC One M8 and the HTC One M9, according to Neurogadget. The issue is no one is certain when, as the Sense 7 User Interface was supposed to hit the M8 by now, and never did.
Like many Android phones, the M8 will probably skip the Android 5.1.1 Lollipop. In fact, this device doesn't even have Android 5.1 yet, so HTC One M8 users can probably count on a decent wait time before Marshmallow comes to the M8.
As for the HTC One M9, only those that possess the Developer Edition have Android 5.1. The news about releasing the latest Android 5.1.1 version on every edition of the HTC One M9 has also not been made public. It is possible that it will just skip the Android 5.1.1 for 6.0 Marshmallow.
So it is not clear when the Marshmallow update will be coming for the HTC One M8 or the M9. There is news from Android Central that AT&T is pushing for an update that will patch the Stagefright problem. If you aren't familiar with Stagefright, it is an exploit that can run deep in the Android OS, and it will come to your device in the form of a video MMS file.
The LG G4, LG G3, and LG G2
As for the LG smartphones, there are a lot of rumors going around like on Australia Network saying that the LG G2, G3, and G4 are going to be skipping the Android 5.1.1 Lollipop update and just skipping to Android 6.0.
This rumor has also been reported on Neurogadget, as there are a lot of cues that reveal that LG might be passing up the Android 5.1.1 Lollipop update for the LG G series of smartphones and just "wait it out" until Android M gets released. This actually makes a lot of sense from a business standpoint, but from the point-of-view of a typical user of the LG G4, G3, or G2, it means a lot more wait before they receive the latest version of the Android operating system on their device.
LG has skipped other Android updates in the past such as Android 4.4.4 KitKat and Android 4.4.4 KitKat. This is different than what Samsung does, which is consistently update its devices with the latest of Android versions, even though the rollout might be slow.
As far as the older models of LG phones are concerned, it would appear that the LG G4, the most recent version of the G series of smartphone was lucky enough to come with Android 5.1 out of the box. However, even this phone, which was just released this year with that recent version, probably won't get Android 5.1.1 but wait for the Android M. There is news that there is a way to extend the battery life on the G4, according to Android Central.
G4 and G3 owners will get their latest update to Android M even with the wait. However, those that are using the LG G2 might not even get Android M, but it is possible that you could receive Android 5.1.1. In fact, there is a report from GSM Arena saying that the LG G2 could be on its way out.