Some say it's better to leave it on stock with KitKat because it works great, the Lolipop update screws up battery life.. so do you think it's better to leave KitKat and to not update it?
I think it depends on your needs. Personally, there are some Lollipop features that are worth the quirks. I can always carry a small external battery, and with a quick charger in the car, its not really an issue.
I had a great working Stock TMO M8 with 4.4.4 but the stock 5.0.1 had bad battery life..
As a result i made my unit a GPe with 5.1 and its back to better battery life.
So im thinking its probably carrier dependent if lollipop got messed up or not.