There's not a terrific answer for this, D.J., or at least there are a LOT of answers which may or may not suit your situation.
Here's the low-down:
An agent exists for the purpose of using their contacts in the publishing world to sell a book and to represent the author in contract negotiations. They get paid from 10% to 20% (most often 15%) of any money the writer makes. Most agents used to BE editors somewhere -- otherwise they wouldn't have contacts in the publishing world and are of little use to you. Good intentions aside, if an agent can't get in the door of a publishing house any better than Joe NewbieWriter can, then why bother? BUT, as I said on another thread, an agent plans to pay his (we'll use this for gender neutral for the moment) own salary with the money he earns from YOUR book and the books of others. He also has to pay the office rent, the equipment leases, the secretary's salary, etc., etc. So an agent is, by necessity, much more picky than an editor. They can't AFFORD to take too many chances on books. If they can't immediately think of one, or even three, good homes for the book, they'll move on to the next manuscript.
An editor exists for the purpose of making the PUBLISHER money. They get paid a salary and whether or not your book does well in the market is of little value to them (except that they try to get promotions and raises by finding HOT TICKET books that sell millions! I would have LOVED to have seen the look on J.K. Rowling's editor's face when the first sales reports came in!) But publishing is a crap shoot and editors know it. All they can do is use their best efforts to try to find a good book that the public will hopefully like. So, they're more willing to take chances.
So, you have to ask yourself: Do you understand contracts, and can you negotiate your own terms accurately in the industry? Do you KNOW what rights you're likely to get and what you should give up? Should you allow the publisher to option your next book? How would you write the remainders clause?
If you don't know the answers to these questions, then you should do one of two things: find an agent first, or find an entertainment attorney and skip the agent to go directly to the publisher. An agent is concerned with your CAREER as a writer, whereas an attorney is not. Specialty attorneys, such as ones who practice entertainment exclusively, are very expensive. They charge upwards of $250 an hour (mine is $350.) I use both an attorney and agent in some specific situations and one or the other most times.
Neither decision is BETTER than the other. It all depends on you and what you want. Not much help, I know -- but it's the best I can offer.