I started out flying mode 1 in Asia, when I was still young. I then picked up mode 2 after buying a new radio in the U.S.. The transition wasn't a big deal especially since I had never fully mastered mode 1. Today, I could still fly a mode 1 airplane, but would struggle with a mode 1 heli.

With regards to which is preferable, I personally think mode 1 is suitable for airplane 3D flying, while mode 2 is suitable for helicopter 3D flying.

It is just easier to twirl the rudder/elevator stick in mode 1 for flying rolling harriers (plane), just as it is easier to twirl the cyclic pitch/roll stick on mode 2 for piroflips (heli). Trying to coordinate a circular motion across two sticks is sloppy at best, not to mention any accidental input to the remaining 2 channels.

Now there are guys that fly mode 2 that do perfect rolling harriers, and there are mode 1 heli pilots that can piroflip as well. But given enough practice and talent, humans have the ability to adapt and overcome most shortfalls. It doesn't mean what they're doing is ideal, nor intuitive. Mode 2 heli pilots still do the fastest, lowest, most precise piroflips hands down. I've seen exceptional mode 1 pilots do piroflips as well, but they're just not the same.

Maybe one of these days I shall go back to mastering mode 1, and fly only airplanes in that mode.