I've been boxing since 2007, and have been training in the same gym until 2012. Stopped training for 2 years because of work, but tried to come back since May of last year. I've been travelling around for the past year, and worked in different gyms. For the first 5 years of training, I was taught to throw the left hook with my palms down. But for the past 15 months, half of the gyms told me to punch with my thumbs up, and half of them wanted me to stick to palms facing down on the left hook. So is it better to throw the left hook with my palms down or thumbs up?