So far I've found the B-Wing to be the best for it for a number of reasons:
It can move slowly to keep the range open for as long as possible.
It can turn tightly to bring new targets to bear.
It is survivable.
It is relatively cheap which means that you won't have to build your list around it.
As for the other options mentioned:
The Lambda is cheap but it can't hang around for long before it has to begin a big slow turn around.
The Firespray is decent but you're not getting the benefit out of the rear arc that you pay points for. Krassis is decent but I doubt I'd put it on anyone else.
The Defender is too expensive. Adding a HLC to it forces your build to revolve around it, and at the end of the day, it is not much harder to kill than a pair of TIE fighters. It is also lacks the ability to duel in close.