Consistently good workout, always leave in a sweat. Able to adapt to high or lower intensity (walking vs run).
I especially like Ahmad as a trainer. His music is always motivating and intensity-appropriate. There are other trainers who use uninspiring music or when the workout calls for going 'all out' the music is more suited for cool-down. Also, he is quick to offer alternative exercises when you are not able to do the one that is given. He should give lessons on how to choose workout music.