I find dismounting at a block is the easiest way, but make sure someone holds your horse for you!
I try to dismount conventionally as much as I can, because I feel safer doing it. However, I occasionally slip my hip when riding, which means I physically can't swing my leg back, so I need several helpers - one to hold my horse, one to help me manouver my legs, and a third to catch me as I slither off!
I will admit that I told off a friends' boyfriend for swinging his leg over the horse's neck once. He was just learning to ride (fortunately on a quiet type) and decided that he was John Wayne

Without warning, he flung himself backwards in the saddle, one foot over the horses ears, and threw himself off

Fortunately, he landed on his feet and his girlfriend was leading him so someone had hold of the horse, but I informed him, under no uncertain terms, that had he done it on many other horses, the sudden movement of his leg towards their head would have been enough for a freak-out, and he would have been in no position to stay in the saddle.