My KDF tac loves her Bortasqu', Kar'fi, Mirror Qin, and the Chel Grett.
Mirror Qin and the Chell Grett if you have it are the more "standard" options. They fly like escorts. Go fast, use DHC/turrets, hurt things. Both are nice, I give the edge to the Chel, but the Qin is more maneuverable.
Bortasqu' is a total beast, but she isn't for everybody. She barely moves better then a Vo'Quv, but once you learn how to handle big ships I've found no more fun cruiser. She is like the Dreadnought Cruiser on steroids and taking graduate classes in pain. A totally different playstyle, and an expensive option, but worth it if you know how to fly one.
Kar'fi is a PvE powerhouse. You will always have another option. You get the entire KDF fighter force to choose from, and some of those pets are amazing. Interceptors? Slavers? Fer'Jai? Oh my! Commander sci slot can stack with a tac's captain abilities to do some crazy things to the power of a grav well or TBR. She has an escorts weapon layout, a significant amount of tactical abilities, and a turn rate that makes all the other full carriers jealous. She also looks amazing. I love cruising around with a full complement of S'Kuls, with our red engine exhaust trailing... I like her better then the Vo'Quv, even tho some people say the Vo'Quv with BoP bets beats it out... maybe it does for the sci's but I prefer the Kar'fi on my tac.