If your transmitter has an internal mixer you will want elevon mixing (all on the right stick, or throttle and wheel in this guess im guessing). Again, a thing of personal choice but vtail mixing is using the elevator and rudder channels (vtails are a type of tails on rc aircraft). If you are using an extrenal mixer either will do as you cna choose which channels you plug them into on the receiver.

50/50 means that when the stick is at rest, it is exactly half way between forward and reverse. 70/30 is great for cars as it provides 70% of the travel (so finer control) to the forward function on the car and only only 30% to the less commonly used reverse. A way to test if your transmitter does this is to put a servo first on the steering channel and put the servo horn exactly in the middle, then put that same servo on the throttle channel and see if it stays in the middle when the throttle lever is let go.

as far as i know, all external mixers do the same thing. Stay away from ccpm mixers as these are for helicopters and do something entirely different. And are also really expensive lol.

Hope that helps , sorry if it was a bit confusing hehe

edit: it badly needed proof reading hehe