The subject line should really be something like, "Less Experienced vs. Established Agents" but here's the question.
A lot of never-published writers, myself included, think maybe I'm more likely to get a hearing -- a reading, really -- from a younger, less experienced agent, that someone still building their list is more likely to take a chance on an unestablished talent than a well-established agent with a big backlist who can pick and choose very selectively who he/she takes on.
But then we think, a more established agent is more likely to have better contacts among editors, more likely to know which editors can be persuaded to buy the book.
The question really boils down to this. Since agents are to some extent competing with each other, how collaborative are agents in one firm with another? Is the young and inexperienced agent who takes on my book going to get a lot of help and advice from senior agents in the firm or will they be reluctant to be too helpful in steering the young agent towards the right editors, since that might make it more difficult for them to sell a potential project of their own to the same editor (siincd there's a limited number of books any publishing house can buy). Do the agents within a firm really work as a team towards the overall success of the firm, or are they really lone wolves who do enough, but just enough and no more, to help the overall effort?
To break down a couple different issues here:
(1) Older agents do take new work if their old work isn't selling. Agents who have some huge estate and aren't actively agenting don't accept new submissions and sometimes don't bother to appear on agent rolls, except when someone hunts them down and puts their email up on a website. If an agent is accepting new material, send them new material.
(2) I can't speak for every agent team that has younger members, but my agent (my agent agent, not my boss who is an agent) is part of a team, and she is very young in the field, but the senior agent clearly has a hand in the financials of the business and hired her because he trusts her judgment and would help her out if she needed it. I used to work for an agent who had two sub-agents, and one was more independent than the other, but both could ask the top agent for advice.
Then there's groups of agents and there's agents with sub-agents. An agent with a sub-agent takes a cut of the sub-agent's earnings while the sub-agent learns the trade and uses the head agent's resources, so the head agent has a huge stake in the success of her sub-agent. My boss used to be a sub-agent, and when she had enough clients she split off and now has her own successful agency, but some older business still goes through the old agency she worked for because of contractual issues. For multiple agents working together, they do tend to share things - that's why they're working together. That or to save on rent on office space, which is a huge deal and a good reason to join a large agency in NYC. Either way, people in the same office have a vested interest in seeing the others thrive, so if you are applying to a sub-agent or a new agent under an older, more experienced one, I wouldn't lose a lot of sleep over their age or experience.