Nuclear engines are heavy, and on average have better armor, their thrust is on par with Chemical engines, but they have about twice the efficiency, they also produce a moderate amount of electricity.
The Plasma engine is quite lightweight and has very high fuel efficiency, but also produces much less thrust than Nuclear or Chemical, it also produces no heat and uses massive amounts of electricity.
The Chemical engine is not exactly a mid ground between the other engines, it's thrust is the same as Nuclear engines, but the Chemical has the highest fuel consumption. The chemical engine has a mass of about half the Nuclear engine and it produces a small amount of electricity.
At first glance the Chemical engine appears pretty poor with it's massive fuel consumption, however it is capable of airbreathing, so if you fly in an atmosphere with suitable gases it's efficiency will increase greatly, making it one of the best engines for use in atmospheric flight.