The picture below is of my old Logitech wireless keyboard, it lasted a LONG LONG time before it finally died on me. Truth be told Pepsi had more to do with the failure than Logitech.
Logitech wins again with the MK320. Best part is, it's another great keyboard and mouse combination.
Yet another Logitech, this time the MK710. Another great keyboard and mouse combo.
I use much of the same steps as picking a wired keyboard, I don't like ergonomic keyboards, I prefer the simple straight setup. How the keys feel when pressed is a big thing for me, they should have a smooth clean feel. How loud the keys are is important as well, keys that are super clicky aren't very relaxing.
As with a wired keyboard, I prefer a volume control and media controls. What really changes here is the reception. I've had extremely good success with the Logitech Unifying technology. In the past I'd tried others but found even with the receiver on my computer which has a build in desk department it was too far to work properly all the time. When in doubt if trying something new, read the reviews, reception will come up here in a hurry.