But always remember, you're buying what IS. Don't buy a promise that's 6 months away, because you'll never get a refund when said promise is broken.
It is not the promise that has value, it is the reputation backing the promise.
For example, Samsung has walked the walk with Android and has shown a commitment to updating their old phones like the S3 to Kitkat. You buy a Samsung and you will get updates most likely. That is why when my wife wanted an Android finally my list of acceptable devices was mostly Samsung.
Heck, the potential to get updates is a big part of what I am buying with any phone. Companies like LG or Asus aren't even on my list for how quickly they have dumped devices in the past. Meanwhile, when Motorola got out that Kitkat update for the 2013 X before many Nexus devices that really made my pay attention to their offerings. I started recommending the X outright after that.
The relevance of these devices is not just the specs on paper, but the ability to run modern software. With Android L looking like the biggest OS update since Ice Cream Sandwich I personally wouldn't consider a device that might not get 5.0 or 5.1.