Rob and Kev were actually standing on the bridge of Federation HQ in "Erigah"; you just couldn't see them for all the Breen! While they were there, they debated whether or not the Breen Dreadnought was the biggest starship we've seen to date. Other big ships they discussed: the Fesarius (TOS), the Narada (Star Trek 2009), the Romulan Warbird (TNG), the Jem'Hadar Battleship (DS9), the Enterprise-J (ENT), the Borg cube (TNG) and the USS Vengeance (Star Trek Into Darkness).
DIS 5×07 Erigah
Starship size comparison charts
TOS 1×02 The Corbomite Maneuver
TOS 2×13 The Trouble with Tribbles
TOS 1×28 The City on the Edge of Forever
TNG 1×26 The Neutral Zone
DS9 6×22 Valiant
ENT 3×18 Azati Prime
TNG 2×16 Q Who
Constitution class (Kelvinverse)
