Originally Posted by LapLap

Shinjuku is the most crowded station in Tokyo and Ikebukuro the second most crowded.
Only thing is that Shinjuku is considerably larger than Ikebukuro. This dilutes the intensity of the crowds a little, but it does create its own problems as it is notoriously difficult to find ones way around this mega station.

My husband reminded me that although Shinagawa Station is one of the easiest to navigate, the walk up to the Grand Prince Takanawa Hotels and the Marriott Sakura Tower does involve a climb up a moderately steep hill. (It’s a completely flat walk towards the IC Strings on the Konan side of the station). Shinagawa is a bit hillier than Shinjuku, so there is that downside.
Taxis are particularly easy to get at Shinagawa Station though, so this problem can be disappeared for under 800yen. Walk towards the station is all downhill.