Being larger does not make the ship more suited for battle. I might go with Defiant just based on maneuverability and the fact that it has a cloaking device.
Voyager with future armor, okay, but Voyager when it was built loses easily to Defiant.
True considering the Defiant pwned the Lakota. However, IIR the Defiant class was basically the testing ground for everything that got put in the Sovereign's. Enterprise E- is everything the Defiant is but bigger, faster, better shielded, more powerful and has a bigger arsenal of weapons available. Remember, E-E was also constructed to be a Borg fighter.
With Starfleet having possession of the Romulan cloak aboard the Defiant, I am sure it has been dissected enough where starfleet captains have been briefed on how to detect cloaked ships using Romulan cloaks, and how to track them. Heck, even Geordi figured out how in TNG.
Also, Defiant may be more maneuverable, but the defiant is only able to fire forward, whereas the Sovereigns have a 360 firing arc for the phaser arrays. So the maneuverability is not as much an advantage against Enterprise E, as it would have been against the Lakota, or maybe even a galaxy class ship.
Defiant isn't winning this one against Enterprise E.