The Romulans, Cardassians, Klingons, and Ferengi all have very distinct styles of ship design. However, most ships share the same essential elements: There is almost always a bridge, some form of energy and projectile weapons, both warp and sublight engines, and basic living spaces for the ship’s crew.
Beyond unique design styles, most factions also have their own special technologies that are seen as trademarks of their fleets. Both the Romulans and Klingons equipped their ships with their own versions of cloaking devices. The Breen were feared for their unique energy dampening weapon that turned the Second Battle of Chin’toka into a decisive defeat for the Federation, Klingons, and Romulans. There were also non-standard features that were unique to certain classes of ship. The USS Prometheus had a revolutionary new multi-vector assault mode that could turn one ship into three built on older saucer separation technology.
If you were designing a starship, you would have to include all of the standard features in the design. But no ship has room for all of the optional extra technologies that are seen on starships across the galaxy. A ship that was transwarp-capable, cloaked, multi-vector assault mode equipped, and armed with special weapons would likely never hold together. Ships like the USS Defiant show that an over-specialized ship stuffed with advanced technology was an engineering nightmare to keep running.
If you were designing a starship, which non-standard feature would be at the top of your list?