I stayed on KitKat on my Nexus 7, partly because I was using some modifications on the stock ROM (can't recall the name of the system anymore), but also because I read about some N7s failing (as in, not even booting up anymore--more like a hardware failure) after Lollipoop was installed. No issues at all with KitKat on the N7.
I do like the interface of Lollipoop but on both the Nexus 4 phones in the house, it has proven to be unstable. Both shut off for no reason whatsoever. And they have other small bugs that make the phones frustrating to use. I've lived with it, and I've hoped recent OS updates would have fixed those few show-stopping bugs, but nothing has changed. Since I need to keep it at least a few more months until the next Nexus 5 comes out (and provided that new phone is any good), I am about ready to just put KitKat back on it--I rarely ever had a problem with it.
I wish I could have the full Lollipoop interface but still keep the "core" OS of KitKat. I don't load up custom ROMs anymore like I used to. My old Thunderbolt is doing duty as a spare VoIP phone/remote control/music player around the house, and is the only one that has a custom ROM (LiquidSmooth).
Yeah, I'm hoping Marshmallow is more stable, and better supported. I'm willing to give it a try. Although I am thinking for the Nexus 4, there probably won't be a build for it.