When we first moved into our apartment we had a Linksys WRT1200 ACS router in the living/dining room but, even with the high gain antennae fitted to it, we couldn't get any 2.4 signal in the main bedroom (end of the hallway and furthest room from the router), and were barely able to connect in the second bedroom or kitchen (both with walls adjoining the room where the router is)!
After a bit of reseach I opted for an Amplifi HD system, which comprises a main router and two additional mesh access points. Router in the same place as before, and mesh access points in the helpers room (opposite kitchen and adjoining living/dining room), and a second mesh point in the main bedroom. Now we have full signal strength in all the rooms. In fact, we don't actually need to use the mesh points as the signal from the router alone is strong enough to penetrate into all rooms in the flat except the main bedroom en-suite (for which we need to switch on the master bedroom mesh point!).
It looks quite stylish to boot, although it was quite expensive (~HK$3,000) and only managed to find a single shop stocking them in SSP.