in some respects, it depends on your house.`
I've always needed one repeater. My deal is that I put the DSL modem where it needed to go which is close to the NID, about 8' of cable.
The router/wireless portion went in the center of the basement. My initial set-up had a dial-up router/modem with WIFI and I used Ethernet over Power line to get the signal to the basement. Brick ranch house with a basement.
When I looked at line of sight there were big issues. A closet to get to the living room and a shed, earth and cinder block wall to get outside.
In fact, I could get a signal in the living room, but not where I normally sit. It was about 10 feet away. So, I installed a repeater. It was 802.11b at the time.
I'm not happy with what I have now and I have a TV which doesn't like multiple SSID's.
if you want really good coverage, a mesh network is the way to go.