For me I have always liked the Spads. Recently Ive really started to like the Spad XII. Its sort of an oddity. It has a single .303 Vickers machine gun firing through the propeller plus a single 37mm Puteaux cannon firing through the propeller shaft. The Puteaux was a tank cannon shortened and adapted to the Spad. It was a single shot gun that had to be hand loaded. Since the breach of the cannon was sitting between the pilots legs its obvious that a regular "stick" control couldnt be used. So the Spad XII used Deperdussin controls. These were similar in layout to the controls used on the P-38 or most bombers where a wheel controls the ailerons and moving the yoke controls the elevator. It had a Hispano-Suiza 8Cb, liquid cooled V8 engine producing 220 hp driving the propeller through a reduction gear. This had an advantage to other designs using rotary engines in that the pilot didn't have to deal with the large gyroscopic forces resulting from spinning the entire engine.
Other favorites of mine however are the Sopwith Camel and Pup for their rotaries! The rotary is unique and almost unknown and unheard of these days. Noone ever imagines that you could solidly attach the propeller to the engine and then spin the engine and prop together! This allowed for some wild handling and quick turns... in one direction however. The rotaries of the time had a high power to weight ratio plus were very intriguing (at least to me) with their poppet valves located in the piston, no throttle to speak of (using a blip switch) plus all the castor oil!! Pretty cool stuff!!