I would avoid the 6 plus as it has an issue with touch responsiveness as the unit gets older. But the 6 is still a great phone.
Issues reported with this - but seems to be mostly avoided by securing the phone in a rigid case and with some sort of screen protector. Flexing is causing some soldering to come loose on the screen, on some 6 / 6+. Build quality Apple is not really wanting to discuss (quelle surprise - their usual go-to) - but I have a 6 (in a rigid battery backup case) and not (yet) experienced any issues.
As for sales - Apple yanked the 6 / 6+ from their stores in North America the day they announced the 7, essentially making the phone 'obsolete' in their minds. If you are thinking of buying thru your phone provider, anything over $0 over the course of a contract is too much - but yanking it from their Store means it essentially has no retail value, as far as Apple is concerned. But you can, of course, get AppleCare+ with this 'new' phone from a provider or, I suppose, any 3rd Party distributor.