In FS 1, the Dragon was the worst there is for sure, however in FS 2 the Mara isn't really such a killer (especially when you get your hands on an Erynies or Ares... Hell, even a Perseus with quad Kaysers can outhandle and outshoot a Mara), and the Dragon doesn't have enough missiles to really be a pain. Also- Trebuchet-killing Dragons is pretty satisfying. The heavy fighters can be Maxim-sniped by a wing of Boanergeses if they warp out 3 klicks away before they can do a thing. Then there's the Astaroth, but that would pwn and own only if it was stealth because it's too delicate. Therefore- no winner during the SSI.
In terms of bombers- the Seraphim, followed closely by the Nahema, which after breaking off it's attack, is a tough nut to crack in anything slower than an interceptor, or with less firepower than an Erynies or Potato.