I had some wifi issues in the house and while I will use wifi repeaters, the first port of call should always be
(a) Examine whether your wifi-channel conflicts with your neighbours wifi.
(b) Ensure the router is not buried down in an old cupboard and is situated in a central area.
However, I was an Asus RT-N66U (Dark Knight) on ebay and since I had already seen one at a friends place, I went for it. It came it aftermarket (bigger) aeriels and tomato firmware.
Now all my devices get a decent wifi signal 🙂
However, if you do need a wifi repeater, I use TP-LINK TL-WA860RE wifi repeaters and they are great.