Kill it and kill it now! The Seraphim poses too great a danger to friendly capital craft to be allowed to live. If any Shivan bomber in a mission is going to be carrying high-yield bombs like the Helios, the odds are very good it's going to be a Seraphim. Even if they aren't, the Seraphim has enough capacity in its secondary banks to do serious damage to anything short of a juggernaut. Seraphim should be the number-one priority for any interceptor pilot.
This Shivan equivalent of the Ursa, or Sekhmet is tough and deadly, and a serious threat to everything ranging from cruisers to superdestroyers.
Try flying this. It is surprisingly fast and maneuverable. Gunpoints are lousy though, being unable to hit anything smaller than a cruiser, and even then you can miss.
The Seraphim is an intercept pilot's worst nightmare in FreeSpace and FreeSpace 2. It's so strong, it can tank paired Trebuchets head-on! Its turret mounts are all over the place, meaning that regardless of where you attack it from, you'll definitely have to take a few retaliatory hits. If you encounter any of these, and you have Trebuchets to spare, hit it at long range with four Trebuchets. If you can't do that (or you don't have any), close in upon it at two clicks, augment your front shield and start firing like crazy.
An alternate way of killing Seraphims quickly is to concentrate your fire on one quarter, brining down its shields rather quickly. Then scrap its hull to tiny pieces. This tactic is applicable to other bomber types, too, but the heavier the bomber the more viable this strategy is.
If you're on a slow ship (the Ares or Hercules Mark Two stands to mind) and for some reason you're low on or can't carry Trebuchet missiles, an anti-shield cannon (mainly the Prometheus S) and a Maxim can work really well if you focus on one quadrant.
This is a terrifying bomber to be sure. I once made the mistake of flying in front of one... That didn't end well. It carries an obscene number of bombs, has a ridiculous amount of shielding, and its hull isn't exactly flimsy, either. Luckily, this thing's the size of a small mansion, so missing it is virtually impossible.
Beware of the turret. On higher difficulties it will slowly work away at your shields, and interceptors don't have a huge amount of shielding. The amount of fire required to bring one of these down is enough for it to almost completely deplete your shields. Throw everything you have at it. Harpoons when the shield is low will do quite a bit of damage, if not outright killing it. Of course, you could just move out of the firing arc, but I get confused by the shape.
Curiously enough, a pilot who knows his ships will know that the Seraphim has an interestingly close resemblance to the SF Manticore in general shape, which brings me to the only flaw I could ever find with this bomber: The shape and size make it easy to hit, although its shields and armour are so thick this trait is barely a flaw at all. Also, I've found that killing it from its left, right, or underside is easier, simply because this ship has too many turrets.