If you were to gather a group of 100 IT consultants and pose this question to them, you would likely receive 100 different answers.
Bottom line is that if the house is large (2000sq’ or larger), or has thick walls (such as adobe), metal mesh in the walls, or significant metal objects in many of the rooms (metal cabinets, refrigerator, TV, etc.), chances are a single wifi unit will not do the trick.
If this is the case, you have two ways to go. You can use a mesh network, using several wifi devices placed around the home connecting wirelessly to the primary base station. This has the advantage of plug and play. This has the disadvantage of very poor overall speeds.
The other option is to have a primary wifi base station, connected via ethernet to multiple wifi access points throughout the home. This provides excellent coverage and speed, but you do need to run the ethernet from each access point to the primary.
Personally, I would never choose option 1. Over the years I’ve had too many clients go this route, only to tear their hair out with frustration over poor performance.
My current personal favorite is the ASUS RT-AC5300 as the main basestation. It simply rocks when it comes to bandwidth, and has among the best security in its price range. Then for the access points I'd use the ASUS Dual-band AC1900 Repeater.