Right side for me. I’ve had/trained two labs. Both on the right. I toss training dummies with my left arm. …Would’ve conked the dog over the head every time otherwise. Didn’t want to cradle and hold my gun over their heads either. Worked great for me as a lefty, but hard core trainers didn’t like it. I never tested my dogs, but should’ve. I’m not sure if hunt test rules require left side or not, but my dogs were both on my right everywhere for me and it worked perfect.