Airline Club

I am a new player, but based on the stats, I would say the A318 is far too expensive for the number of seats, and it has way more range than you need for most domestic routes.  The Boeing 737-100 is very cheap by comparison and has almost as many seats, though it burns more fuel.  The 737-700C or Bombardier CS100 would be a good replacement if you need  long range and good fuel economy.  If you want a bigger plane, consider the MD-81 or the A20.  In real life I think 737s and A20s are very popular, but I don't know what is best in the game.