Nexus 7 2012. Ran perfectly on 4.1 Jellybean, then each update gradualy made it worse until KitKat which was excellent.
5 was ok but kept freezing. 5.01 improved it slightly, then 5.02 ran great as long as I force closed apps after having about 5 running.
Now it updated to 5.1 and even if it runs ok, after an hour on standby and not running anything it hangs when turning it back on. Consistenly until I reboot or find out what app process has eaten all the memory away.
As M has been stated to not be available for N7 2012 I'm going back to KitKat and sticking there.
(Oddly 5.02 on my Moto E 2nd gen LTE is brilliant)