I fly both airplanes and helis as im sure alot of people on here do. I learned on planes first, this helps get your orientation and reaction down. What i mean by this is knowing what way to move the stick when the model is comin at you vs going away from you. When i learned how to fly helicopters, it was a whole different learning curve. however once the one with the big spiny thing on top was flyin around in the air, it flew alot like a plane. with a heli you HAVE to learn how to fly with the rudder. once you learn that and it becomes second nature, you'll notice you do it when you fly planes too. you have to always be on top of a chopper to keep it in the air, where a plane you kinda point it in the direction you want to go.

As far as answering your question, planes are easier. i learned how to fly a plane in a day, where a heli took me a couple years to get the extra tools, save up to fix my crashes ( i was 15-16 at the time), and to build up the confidence to try it again.