As mentioned...stick with a plane...it isn't just coincidence the most deadly players always fly the same aircraft(s). I know what newbies think..they take a Spit up, get owned by a Niki, then say to themselves, "Damn, that Niki is a good plane". So, next hop they take a Niki up, then they get whacked by a P51 and the cycle continues. It's not the plane that killed you, it's the guy flying it. He knows his plane better than you know yours and simply used that knowledge and your lack thereof to his advantage.
I know some get bored flying the same plane. So, if you are one of those people my suggestion is to pick a perk plane, a sub 10 ENY plane and a sub 20 ENY plane to get really good at and stick with them. Then you will have one to use in every situation. I would also suggest not mixing gun platform types. By that I mean pick either wing mounted gun package planes or nose/cowl mounted. The reason is, the mental aiming process is subtlety different between them and adapting to that from one flight to the next compounds the difficulty of success exponentially.