TOPIC:

My 19"s have done nearly 20,000 miles; 3-4mm left on fronts and 4mm on rears, on 1.6dCi 4WD which I leave in Auto 4x4 (no point having a 4x4 and running it in FWD). The Contis seem to pick up every stone in the road and tell me about it whenever I open the windows. I would have preferred 17"s for choice and price of new tyres, but I have had no problem with the ride at all. 

My 2wd drive still has 6mm left on the rears but less than 2 on the front, kind of balances things??

I thought about the OPs original question, I'm still asking myself but have the experience of having owned both.
I'd say if you want a more comfortable ride and want to ignore speed bumps, its the QQ, it simply has a softer set to the suspension. Iif you want a simpler but more reliable/predictable infotainment console it's still QQ. Kadjar is still the prettier and somewhat less common, numbers on the road make the QQ seem very common place.

Swings and roundabouts/pros and cons, personal preference must rule, don't buy without trying both as no one knows what you will prefer as can be seen from all the various comments,

I suggest, we make difference between RLink version 2 and 3. The fact, that version 2 is full of bugs and crap, does not mean, it's the same in version 3, which I find basically flowless! If the guy's gonna buy a car made after May 2017, all the criticism does not count for the RLink. 

Firstly I'd like to thank everyone who's taken the time to post replies. It's been very interesting reading about your views regarding the tyres, an issue which did concern me as I had seen various reviews which encouraged getting the 17 inch over the 19 inch wheels. The debate about the infotainment system, especially the most recent post by Aone, has encouraged me as I had heard the RLink system was a little quirky.
In the end I have ordered the Kadjar albeit with 19 inch wheels, I have bought the car through an agency which has given me a 33% saving on the list price but no choice on wheel size, so with the money I've saved being able to go towards paing for new tyres and the fact that French roads are considerably better maintained than UK roads, I'm hoping the tyres will last a decent amount of time - oh yes, and also as of the 1st July the speed limit on the vast majority of the country's 'A' roads is now 80kph (50mph) so I won't be going anywhere in a hurry.
Another major factor is that in France you're never far from a Renault garage but there are comparatively few Nissan ones. I would appreciate anyone's advice about whether they respect the advised service intervals for the KJ, every 20k or 2 years seems a little long.
As always there are compromses, I wanted a CD player because I'm used to having one and have c 300 CD's to choose from but I'll have to rip them all and get used to using a USB key. The KJ doesn't have the same rarity appeal in France as in the UK, in fact I have yet to see a new QQ over here but KJ's are very common. The size of the boot of the KJ is another winning factor, the new QQ boot, esecially with the Bose sound system, is quite small. And little things like the parcel shelf and the number of USB ports also helped me make up my mind.
I have no doubt I shall be back on the forum once the car arrives and I find that the French handbook doesn't have the answers I'm looking for but in the meantime thans again for your help in steering me towards the KJ.

Offtopic:
I don't understand your government. In Austria the speed limit is 100 km/h on A roads. You rarely feel you've been limited more than normal and most of the people drive with the limits. Going through villages with 80 make you even drive slower than the speed limit. It's a pleasure driving in Austria. On the opposite side is the neighboring Italy. Everywhere - unnecessary and frustrating speed limits and guess what - NOBODY drives according to regulations and signs. Just like in my home country - Bulgaria. I thought we're the worst, most arrogant and mindless drivers ever, but the Italians beat us totally... So... my point is - we're 2018. The regulation should be upgraded and the less you limit a person, the most strict he will be. Doing the opposite, just make you don't give a damn about signs, law and things like that....
C'est la vie...

I had a 6 CD-changer in our last car, that I thought I would miss. Not the least! It takes a little time to rip the CDs to Mp3, but on the other hand, you can bring your whole collection on just one stick. Me and my wife have a stick each, with all our favourite music. About the wheels, I guess you'll be fine with the 19" in France. We had a very smooth ride there with ours, as opposed to some parts of Eastern Europe. Enjoy your Kadjar - I do.