Davion has the edge in raw firepower, speed and armor, and can out-bracket the Naga at least.
Bracketing raises another possible variable: can the Davion use Bracketing Fire Mode? I know some players interpret the sentence at the start of those rules "
A skill lost during the Star League (along with the top-secret algorithms that made it practical to employ)... " to mean that bracket fire was a SLDF navy, and perhaps HAF navy (which seems to have still existed during the Star League according to the Naga fluff), ability not known to the other states, all part of the Hegemony and League's longstanding technological edge.
If that interpretation is used, and the Baron is determined to be in the SLDF or HAF fleets instead of one of those transfered to the member states, then it gives the Baron and Naga an advantage at longer ranges and increases their ability to cope with poor electronic warfare rolls.
That said, even if the Davion is denied the ability to bracket, given its thrust advantage any edge the Baron and Naga possess at longer ranges isn't going to last, although it should be noted that to close the range the Davion will need to point its bow towards the enemy, presenting the possibility of a nice juicy nose crit if it does so while in range.
Overall, I think the Davion will win more encounters than it'll lose, but I can see some useful possibilities for the other two. With either the Baron or Naga, I'd attempt to keep the Davion in my broadside/aft quarter overlap, allowing me to attack with two decent arcs aided by the capital missiles using Preprogrammed Waypoint Launches, plus it'll give me a heading partially away from the Davion, helping to keep the range open for a little longer. The Naga does have heat issues, but it's not difficult to work out the maximum damage possible for the arcs fired, and in the broadside/aft quarter you can still be throwing 56 point salvos plus the missiles. Barring poor control of the Davion or lucky crits though, I don't hold out much hope, particularly if the Davion snapshots its nose around for a killing blow - those pair of 50 point NAC bays backed by one and probably two 18 point NL bays can potentially shred the Terran designs in one salvo, either outright destroying them or crippling them.
For a Naga vs Baron fight, I'd favor the former if the above SLDF/HAF-only interpretation of bracketing is being used and the Baron is a transfer, but if both are equal on the bracketing rules, then it becomes more of a toss up. The Naga has the potential of achieving more threshhold crits due to its larger number of bays, and also could achieve more crits once the Baron's armor is down, plus its strong SI enables it to survive longer thus giving it more time to hurt its foe. The Baron has superior bracketing capability and while it will likely get fewer threshhold crits, it'll be hitting SI sooner, with that big broadside NL bay in particular guaranteed to be chewing through the Naga's SI with every hit. Overall, with equal bracketing availability, I'd still give the nod to the Naga, but it's marginal and it'd be a fight that could change with a single dice roll, plus I doubt there will be much Naga left to savor its victory.
With fighters involved, the questions are what fighters and how many does the Baron get? Give a SLDF ship in this matchup a squadron of Hellcat IIs and the electronic warfare battle suddenly becomes very one-sided against non-SLDF, which can have a big effect on the long range fight, especially if using the SLDF/HAF-only bracketing interpretation.