Bart,
Concerning gimbal control what is most important is comfort. You don't want something in your equipment or use of it that makes you think about what your doing down there. What matters most is your eye on the model and your input/reaction to flying it.

I advise beginners to use index finger and thumb. Two fingers make you more steady and precise. But, many people have trouble holding the radio when they do this. Transmitter trays & neckstraps tend to help if that is how you want to fly. But, if you just can't get used to it then by all means fly thumbs. Just give the index/thumb method a good solid try. It takes a little getting used to but is indeed a more sure way of control.