Definitely the 86u. Just had a look on Amazon and they are the same price so if I had to make the decision now I would definitely get the 86u. Apart from the improved wifi, the wan to lan throughout is markedly better at 940mbits vs 740mbits on the 68u and I don't think those speeds are as far off as some people may think. We have got 500mbits now and I sure we'll see 1gbit by the end of next year when they start the docsis 3.1 rollout. Other than that feature wise they are pretty much the same. Tbh even if the 86u was £40 more I would still go for it for the reason I stated above plus the way things are going with more and more devices becoming wifi compatible, wanting internet access (need a router that can intelligently handle the traffic and requests) and can process traffic at greater speed. With 5g on the way I think wireless devices/clients are very quickly going to catch up with the speed routers can offer.
https://www.smallnetbuilder.com/wire...outer-reviewed