Newer agents can be great, but I would personally only go with a newer agent if they were working in an established agency. Often, newer agents in established agencies have more experienced mentors who can step in or help out when needed. Also, established agencies often have contract managers.
If someone's set up their own shop with only a few years of agenting experience, it would make me nervous. Mostly because there's a high rate of turn around in this business, because agenting doesn't pay a lot--especially in the first few years. If a newer agent in an established agency quits the business, often the agency will assign you another agent. If a newer agent who set up his/her own shop suddenly quits the business (and it happens) then it leaves a lot of writers out in the cold--and often their books, too, if they're still on submission. Now, there are a few exceptions to this: my own agent was not an agent before starting her own agency. But she had 20+ years experience as an editor at Macmillan and had worn basically every publishing and editorial hat you could. She had all the connections and knowledge already and she became one of the top agent in kid's lit within a few years of opening her agency. So she was a pretty safe bet :D
Even if an agent has thirty deals, it's more important to look at the KIND of deals, rather than just the number of deals. One agent could have 30 deals, but 25 of them are to smaller presses who take unagented submissions and don't offer an advance, and only 5 of them are to bigger, advance paying publishers. Another agent could have only 15 deals, but half of them are six-figure, multi-book deals to Big 5 Imprints and the other half are foreign deals for those books they sold so well in the domestic market. There are a lot of factors to consider, when choosing agents to query. If you don't have a Publisher's Marketplace membership, I recommend getting one for the months you research/query (it's $20 a month). That way you can see all the deals that the agent's you're interested in are reporting, and see what imprints and editors are acquiring from them.
It's also important to keep in mind that an agent's job extends far beyond contract negotiation. They manage your career, they're your cheerleader, your biggest advocate. If the publisher gives you an awful cover, they can step in and try to fix the situation. If you and your editor disagree on changing a huge plot point, you can talk to your agent about the best way to talk to your editor about it. If your book gets pushed back over and over, an agent can step in and be like "What the heck, y'all? You're not treating my author right." There can be a lot of hiccups on the journey to publication, even after you get a book deal. Your agent is the one who helps smooth the way.