Casper Smart says Jennifer Lopez ''crushes on'' every dance routine he gives her when they're working together.

The 28-year-old dance choreographer is in an on-again, off-again relationship with the 'Booty' hitmaker and he loves the 45-year-old singer's creative positivity, which is something she shares with some of his other most high-profile clients.

When asked if the brunette beauty is his favourite client, he said: ''I have a top four. Nicki (Minaj) and I just click really well and I love her music. Nick Jonas is so young but extremely focused and great to work with. Jennifer crushes everything that you give her. Jessie J is like a comedian. She's hilarious.''

Despite working with some of the music industry's top artists, Casper says his job isn't always glamorous.

He told PEOPLE magazine: ''I was on Ariana (Grande's) video for 'Love Me Harder,' and she asked if I could get in the sandbox with her and help her with movement. I completely trashed the $1,200 Louboutins I was in.''

Both Jennifer and Ariana have been accused of acting like divas in the past, and although Casper won't comment on their behaviour he does admit he has a method for dealing with demanding people.

He said: ''As much as you want it to be your show, you're not the one on stage. You can argue your point, but if it gets shut down, it gets shut down, and that's that. You have to handle it with grace.''