The Nephilim and Seraphim are death machines as far as primary weapons go. The Nephilim has only one gun bank, but the bank has seven firing mounts. The Seraphim has three primary banks; a six-mount, a two-mount and a three-mount. Very impressive. Both bombers have two turrets and four secondary banks. The secondary banks on the Nephilim are really small and pitiful considering the size of the bomber, but the Seraphim's are about the same as the Ursa or Sekhmet.
The Dragon and Mara are probably the better Shivan fighters. (original Shivan versions) The Dragon has great primaries - a two-mount and a three-mount bank, powerful shields for its size and unmatched maneuverability. The Mara is simply good as an all-round ship, with very good speed/maneuverability, strong armor and shielding and big secondary banks.
One of the main problems with the Shivan ships is that all the Shivan primary weapons really suck and they use crappier versions of the same secondaries as the GTVA. The light laser fires fast compared to the other two but is still slower than the Subach and does little damage. The heavy laser does twice the damage but fires at less than half the speed, and overall performs about the same as the light. The mega laser does double that of the heavy (Kayser-type damage), but fires even slower, making it not much better.