Gas - Brison 2.4 (I am currently using in my lanier 1/4 extra 300s)

4c - saito 1.8 (provides good power, but loves fuel and shakes a lot)

2c - Moki 1.8 or 2.1 (tons of power - the only reason I chose gas for mine is because of operating costs and comparable weight to the moki's. With gas you will gain fuel efficiency affording a smaller tank to compensate for gas's ignition system)

Hope this helps!