hmm, well i guess for me it would depend on how easy you could field both to an engagement that would require them and if either was better equipped for "Oh F#@K" moments.
-Are either more viable to roam around looking for prey solo vs the other?
-Does the stealth of the Eclipse mean it can disengage for the most part at will and be safe?
-The Ares has the offense, but does it have any chance vs a couple of smaller fighters that happen to catch it?
Lots to find out I guess
For both smaller fighters are the counter to them. While the Eclipse is more stealthy it should be free to engage and disengage on its own terms for the most part, but given this feature is not really fully implemented yet it's still unknown how easy it will be as well as once tagged how quickly will it be to fade away.
Both are also very situational in that you would need to know ahead of time what the engagement is before heading off to it and both would have a hard time addressing any sort of ship outside their specific target role. I would go so far as to say both are not lone ships and are meant to fulfill a role in a group and would be ill-equipped to do so, both in what do you do once you are successful in disabling the target, what do you do with the targets escorts (say attacking a Hull C would be a great target for both ships but no merchant should be flying alone nor would the payday be successful without help from a Caterpillar).
So I would say both are not good for general purpose/ solo game play. Where they shine is in the types of targets and advantage they bring to fleet battles while the eclipse is significantly limited in the number of torpedos it's equipped with it can both be the opening play as well as active in flanking the large/capital ships. Ares is more meant to bring the pain in the middle of battle (along with ships like the Gladius and Retaliator) and engage head-on. So large/capital ships are their targets and fighters are their counter.