Right now, there are only two Sunder setups I've been able to use effectively; my favorite is lance + 2x light needler - lance does long range sniping of fighters, and provides vaguely tolerable anti-armor damage, while the needlers take down shields - and my flux reserves are deep enough that I mostly don't have to care about not having PD. (Plus EMP damage means I can snipe off enemy missile launchers.) This setup makes an excellent flagship for a small fleet.
The other one that kinda mostly works is autopulse + 2x pulse; it's a bit of a bear on flux usage, but it's decent firepower. Works best with some support (or as support), though, while the lance version is much more suited to wandering around on its own.
Should be much better next version, though, with increased flux capacity, increased dissipation, and better HILs and Autopulse lasers. Heck, depending on how the burst mechanics work out, you might even be able to install a guardian PD and not feel like it was a waste of a slot.
The medusa... I prefer pulse lasers over heavy blasters, usually; heavy blasters just eat up flux way too fast, and I much prefer sustainable damage output over burst, run away, vent, repeat. Still, the medusa is fast enough that you can get away with that tactic.
There is one ship I've found that gets good use out of a pair of heavy blasters, even with my combat style: the Aurora. Disregard its missile slots, give it forward mounted heavy blasters & ir pulse lasers, and it's got deep enough flux reserves to just shred small things, and the mobility to back off from bigger targets that might not die in the first pass. (Or you can always mount a few harpoons; a salvo of six of those is usually a solid finisher once enemy shields are down...)