I think I have mentioned this somewhere already, but what about this solution:
Dragon: small light interceptor with A/M engine, capable of catching all UFOs without problem, but with low weapon capacity.
Starchaser: heavy interceptor with ion engines (research based on alien engines. Ion engines use similar technology of magnetic containment and channeling, but without antimatter), in full load, it will be only slightly faster than Saracen's top speed, but capable of carrying heavy payload, acting essentially as gunboat. However, while not requiring AM fuel, its running cost would be very high.
Stingray: medium A/M interceptor, with decent payload and top speed slightly under Dragon's, but with longer range, capable of orbital flight, but with huge consumption of antimatter.