Paul's daughter has a really old router and it's starting to flake out, so it's time to get a new one. Leo says she should get a dual band router that supports not only 2.4 Ghz, but also 5Ghz. She'll want one that supports 802.11ac. The reason to get a dual band router is that everyone is on 2.4 these days, and while 5 GHz is limited and won't go through walls, it is barely used.
Leo advises getting the Archer C7. It's about $80. If money is no object, then Leo would recommend the new Mesh routers, which are smarter and solve a lot of congestion problems automatically.
Leo suggests checking out this article on "Why Wi-Fi Kind of Sucks."