Back in the day I used to have one router in the house: the D-Link DIR-825, flashed with OpenWRT. Configured with two SSIDs – one for internal network use, and one for guest access – the latter being separate from the internal network of the flat.
After moving to our house, I discovered that the house construction materials provide a better shielding for radio signals, which in turn meant that the reach of my WiFi router wasn’t quite what it should be to reach the far corners of the place. I tried increasing the output wattage, but that had only a marginal increase in reach. So in the end I opted getting a new primary router – the TP-Link Archer C5 (though mine has three antennas?), which was promptly reflashed with OpenWRT. The DIR-825 was moved to the opposite corner of the house to increase reach, and at the same time I lowered the output wattage of the radios.
Because of time constraints, I didn’t bother stretching the guest wifi to the second router, as it requires a bit more configuration to properly separate the flows of data between the two networks: vlan configuration.