USS Defiant (Defiant-Class warship)
Pulse-phasor cannons (limited to firing forward), Defensive phasor compliment (covers other arcs, but lack punch), One-shot detachable warhead in the forward section, Ablative Armor, Quantum Torpedoes, Romulan cloaking device, sub-light speeds and maneuverability of a Scout-class vessel like a Klingon Bird of Prey.
CO - Ben Sisko, hero of the Dominion War use to taking on larger ships.
Weaps Officer - Worf, Veteran the Dominion War and Klingon Civil War, has a knack for knowing what to hit to cause the most damage.
Chief Engineer - Miles O'Brien, though a skilled engineer, his strength lies in general systems, particularly Cardassian-Federation hybrids from working on DS9, he is not very specialized in ship's engineering.
USS VOYAGER (Heavily modified Intrepid-class explorer) (Last Version)
Bio-neural Gel Packs for increase efficiency between main computers and systems, Standard Photon Torpedoes, Moderate phasor compliment with decent coverage, Borg enhanced shields, 24th Century regenerative ablative armor technology.
CO - Katheryn Janeway, Borg slayer, bane of the Crenum Empire, and a temporal pain in the a**! Though a skilled officer her tactical strength lies with the ability to quickley adapt knowledge from other crew members into the situation and generate results.
Wild Card #1 - 7of9, liberated Borg drone with memory from the collective. Her extensive knowledge of technology, history, and tactics from the hundreds of races conquered by the Borg allow her to use tactics never seen in the Alpha Quadrant.
Wild Card #2 - ECH upgrade of the Mark 1 EMH programmed with a comprehensive database of military tactics and historical officers that used them. Though the database is out of date, his knowledge of "old" tactics could still provide an edge since they may be able to exploit openings not readily apparent to modern tacticians.
USS ENTERPRISE 1701-E (Sovereign-Class explorer)
Quantum Torpedes, Heavy phasor compliment, and the most advanced systems in the fleet incorperating improved shield designs, computer efficiency, and other Borg adaptions to Federation technology gleaned from Voyager's reports from the Delta Quadrant and detailed study after its subsequent return to the Alpha Quardant.
Jean Luc Picard, Borg slayer and also victor in massacare at Wolf 359. Though his time in the Borg collective was limited and outdated compared to 7of9 his knowledge of the collective still provides an edge.
Geordy LaForge, very skilled ship's engineer capable of making the type of jury-rig modifcations and repairs in the heat of combat to keep the ship in the fight and push systems beyond their limit.
Data, the android would have knowledge of both ships, their crews, and their past tactics noted in crew logs from his studies of various databases. Though he may not seem as intuitive as a human or ex-Borg, his quick mind allows him to proccess countless varables that usually can provide a good guess for predicting what an opponent would do next.
Hmmmm? It would be a VERY close battle, but the Enterprise would win, suffering heavy damage.
The Defiant would not be able to use its older cloak to hide from the Enterprise's advaced sensors and get the drop on her, even if the Defiant could get in the first salvo unanswered, the damage would be minimal against the heavy shields of the Sovereign-class. Sisko is quite skilled at taking on larger ships with the Defiant, but during the Dominion War there were usually several other ships taking on the Jem Hadar and Breen battleships with her. The smaller Defiant was often ignored in favor of the larger more threatening ships like Galaxy-class, Excelsior-class, Romulan Warbirds, Klingon Vor'Cha-class heavy cruisers, and Klingon battleships.
In this battle the Enterprise is more than capable of taking on both ships simultaneously, plus she isn't like a Jem Hadar or Breen battleship, Federation ships tend to have decent coverage in nearly every arc, and the Defiant won't be able to exploit these "no-fire zones" like it could against the non-Federation ships. It won't take long for the Enterprise to score enough glancing shots from the heavier weapons of the Soveriegn-class before it will smash through the shields and ablative armor of the Defiant. Fortunately for the Defiant, Voyager will draw most of the fire and spare Sisko and company from a quick defeat. The Defiant's heavier weapons (compared to Voyager) will be responsible for about 60% of the damage inflicted on Enterprise, before she can take out the smaller ship.
Voyager doesn't have the manerverablity of the Defiant and is a much easier target for the Enterprise. Her saving grace is going to be the 24th Century regenerative ablative armor (The technology was a Borg-Federation hybrid provided by the future Admiral Janeway) and will withstand a lot of punishment by the Enterprise. Though her weapons are outdated and weaker that the other two ships, Voyager will still be able to land some solid hits against Enterprise during the times it focuses mainly on the Defiant. Unfortunately Voyager doesn't have the power to maintain the regenerative ablative armor indefinately and its only a matter of time before the Enterprise's weapons overwhelm the systems defensive capability. Until that point in the fight, Voyager will pretty much be like a f***ing cockroach that never seems to die no matter how may times the Enterprise swats it!
Tactics-wise it doesn't matter becuase the crew and individuals are able to counter each other on a fairly even basis. Its purely a matter of strength and endurance, which the Enterprise has the considerable edge. Its heavier weapons, advanced systems, and the strong engineering skills of Geordy LaForge are what puts Enterprise over the top in this fight.
I like this question. =) It would never happen of course, but it's an interesting tactical question and it got me thinking... =)