In my Scipii campaign I only built a few quinqueremes. I built huge number of Triremes.
The advantage is that these are only 1 turn to build, versus the 2 turns quinquiremes take. So you can quickly crank out an entire fleet, then go back to producing other units. Plus you can repair these at any city with only a shipwright, whereas a dockyard is less frequent, Egypt can't even build them! And since you'll probably get into some nasty naval fights with Egypt, the ability to repair ships (your whole stack of ships even) in a city you have conquered is very nice.