What is the average time for phones to get Android updates?

So I am looking to switch from an iPhone to an Android phone. My main concern is that if I know there is a updated version of an operating system out there then I have to acquire it and shove it lovingly into my mobile device asap. So on average how long does it take to get updates to your phones? If you could provide which phone you are using and under what carrier that would be lovely. This is not including Nexus phones of course. I just want to gauge how good various providers are at releasing the latest versions of Android before I make the assumption that due to my massive neurosis I have to buy a Nexus phone. Thanks.