What acting agency should I audition for?

You don't start an acting career with an agent - you have to have a bit of career going before you can get the attention of an agent. So first you need to get some more training and experience and learn the business end of acting (how the casting process works, what talent agents are and what they do, what casting directors to, how to market yourself, actor unions, etc).

And you should audition for any legitimate agent that indicates an interest in you. In a sense beginning actors don't choose an agent, they choose you. Agents are paid a percentage of what their clients make. NEVER pay an agent up front. Since an agent only makes money if their clients make money, they are very picky about who they take on as clients. And they can be picky because there are a lot more people wanting to be actors than there are parts. So talent agents prefer clients who have demonstrated some level of success rather than someone just starting out.

One way to try to get an agent interested in you is to mail out head shots, resumes and a cover letter. These things will be the tools you have to convince an agent that you could book jobs and make you both money - so they have to be good. Professional head shots can cost some bucks. And you need to have something to put on an acting resume - so we're back to training and experience. It is a waste of your time and money to try to find an agent before you're ready.

A quality acting school/program can help you. It'll train you for acting, hopefully teach you a bit about the industry. It's a place to start networking and getting to know people in the industry that can help you find out about agents and jobs. And some acting schools have a showcase where students perform for agents and you could get representation that way. You might want to consider reading "Acting as a Business" by Brian O'Neil to get a better understanding of things. There are a lot of people out there willing to take advantage of people who don't understand how the business works.

Good luck.

I see from your other question that you're only just looking for classes!

No agent is going to be interested in signing you for at least a couple of years.

You'd need to attend a really good acting school - a cheap one isn't going to be any good. You get what you pay for. Good classes cost money.

You'll also need to build up a really impressive resume by acting in community theatre and student films when you've studied acting for a year or so, gradually working up from one-line roles to leading ones.

Only after that will it be worth looking for an agent.

They're never interested in beginners.

Any agency that says it will accept beginners is going to be a scam.