There really isn't any absolute "Best" pvp ship/loadout around. There are those that are better than the rest, but other than that, it just comes down to each individual's preferences. While one "elite" guy might like fast VHFs with rapidfire guns, another "elite" guy might prefer to go for a heavier choice of ship and slower refires. Even though Discovery is not perfectly balanced and some combos are still better than the rest, it's not like vanilla where nom-tizona Eagle was the only viable choice.
My suggestion is to try different ships and loadouts yourself and see which ones you're more comfortable with, and then pick based on that. Discovery Wiki (despite being somewhat outdated) is a good source to get you started - You can check these pages: Very Heavy Fighters, Class 7 guns, Class 8 guns, Class 9 guns. Generally speaking, cl7 guns have higher refire rate, while trading damage output for efficiency. Cl8 guns aren't as efficient, and generally have a lower refire rate but dish out more damage than cl7. Cl9 guns (also called "Codename" weapons) have a higher damage output than cl8, but are generally slower both in terms of refire and projectile speed.
As for shieldbusters (Anti-shield guns like Debilitators), they're somewhat essential considering the PvP balance in Discovery. With multiple shield classes, your hullbuster guns might end up not doing much damage against certain shields and then you'll end up being a sitting duck, so people generally go for at least 2 debs on their fighters. As for which deb to go for, there are only two available, and their only real difference is their projectile speed, which means it'd be best to go with the one within the speed range of the rest of your guns.
And lastly, for the actual ship - As already mentioned, Eagle and Sabre are both good choices (they're both available to every ID), but that's assuming you prefer lighter VHFs. You can also try Raven's Talon if you want a heavier civilian ship. There are also ships like Guardian, Odin, Nyx, Manta, Templar, Titan and Werewolf, which are all pretty good choices (in their own sub-class) but may not be available on your intended ID, considering they're faction ships. You can check that here (it lists which tech can be used on which ID and with how much powercore output).
