I gotta go with the Vindicator. It is the UBW counterpart of my favorite Thunderbolt VII, with similar capabilities all round. Let's look at the numbers:
Speed: Vindicator has 20kps faster cruising speed, but Tbolt has 50kps faster afterburner speed
Maneuverability: Equal at 50/50/50dps
Shields: Equal at 250cm
Armor: Vindicator has 30cm more armor fore and aft, and 50cm more armor port and starboard
Missiles: Both have six missiles, and the Vindicator has three torps to the Tbolt's one
Guns: Tbolt's 4 Plasma/2 Photon (WC4) or 2 Plasma/2 Photon/2 Meson (WC3) beats Vindicator's 2 Tachyon/2 Laser, but Vindicator has Leech Cannons, which can disable even a carrier with only a few hits, plus the Stormfire Mark I cannon hits hard if you can aim it properly.
All in all, I think that the Vindicator's heavier armor, two extra torps, and leech cannons make up for its lighter main guns, making the Vindicator comparable to the Tbolt. I also think it is quite a bit better than flying the slow-as-a-brick Avenger, which has about the same speed and turn rate as a Longbow, but only half the missiles.