I doubt there is a good answer since so much depends on what
the signal has to get through. I just got a new ASUS RT-AC5300
and it seems to work well for me with pretty strong signals
all around the house.
http://tomhorsley.com/hardware/rt-ac5300/rt-ac5300.html
It may be possible to put DD-WRT on it, but the simplest
alternative firmware is "merlin" which worked well enough
for me and is just the native firmware with a few
tweaks.
On the cheaper side, I made my old router work much
better on the other side of the house using a piece
of aluminum flashing :-).
http://tomhorsley.com/hardware/wifi/wifi.html