I don’t think being exclusive and with only one agency is a smart thing to do in the start of your pursuits.
It might feel cool to have an agency on your side, or to say to someone, “ Yeah I am exclusive with so and so…” but when you are starting to model, it is normal and expected for you to freelance with a few agencies to get your modeling portfolio together.
Then if it does come down to being exclusive I would pick an agency that is getting you the most work and who pays on time and who seems the most into booking you.
Still, I would make your own card regardless whether you have an agency or not. I would never rely on the agency making me a card because then I don't have cards to promote myself with too. You can make a comp card and mail it out to many agencies, magazines, and photographers.
Modeling isn't about waiting these days; it is about having your OWN marketing tools too. So if you want to make a card with the agency and you think they might be able to get you work try it. But don't be exclusive in a rush!
Exclusive can limit your chances for jobs and opportunities.
I work with four agencies. And sometimes one books me, and sometimes the other...I am NOT exclusive.
Sometimes being exclusive can also mean IF you were to book a job on your own or through someone else, that the agency would want a percentage regardless even though they did nothing to help you get that work!
It is normal these days to have many agencies working with you; I think the agency as a marketing tool.
Freelancing with many agencies is normal in the commercial print modeling world.