- Edited
My best is the Drifter - a $500k destroyer with extreme mobility, light firepower, and moderate shielding. It focuses on dodging incoming fire rather than absorbing it, and on delivering precise damage to critical areas.
I'm confident that it can beat 95% of ships in its price range with good piloting. It can also punch well above its weight. For example, it can beat most of the built-in vanguards. The only one it has trouble with is the Crescent Wrath. As long as the Drifter can outmaneuver the enemy, it can kill it, eventually. The scariest I've killed was some guy's $6m ship with 8 giant rails.
Alone, the Drifter is powerful, but as part of a fleet it serves as a quick-response escort for valuable ships and as a flanker to get behind enemies and disable them. Ignore the Drifter and it'll stab you in the back.
The main counter to the Drifter is mass missile fire. It can dodge any amount of missile fire indefinitely, but it can't dodge it all and attack at the same time. It's also vulnerable to ridiculous amounts of small laser/EB fire. Or to anything it doesn't see coming on its flanks; it takes a lot of micro, and a big mistake can mean instant death. For this reason it's best used in small-scale battles of less than $3m fielded, where your attention isn't divided between many ships.