I assume the jets are in HD config
And why the CS series?
in the 2014+, CS300 and A380 are the most fuel efficient jet (fuel burn divided by number of pax) (A380 is more efficient than CS300 a bit), provided that all are in HD setting. But in reality (or in the game world), it's very difficult to assign a HD A380!!! So besides A380, CS300 is the most efficient jet. It really makes the difference (e.g. CS300 vs A319) if the fuel price is about USD 1300 or 1400 (in MT#4).
In those days (fuel USD 1400), my CS300 can still make a profit about 600k per week! (I fly 3 domestic routes per day).
However, in the early 2000s, you can only use A320/A321 if possible, B739/B739ER for the most efficient jet.