One thing to ask is rather you are hoping to make a lot of money or not?
An agent will get you the best deal ever (if you find a good one) but that means you'll have to share anywhere from 10-20% with them. That's where your check will be sent, they'll take out theirs and send you the rest.
Depending on which publisher you get, a lot of production might not go into your book, unless it's deem as a real seller. Your book might get publish, get into a bookstore and that's that. It'll be up to you to advertise and promote your book. If the publisher does it, again it be something small that will come out of the profit you'll make.
Because it is your first book, I'll say go with self-publishing first. This will allow you to do things your way. A lots of work but you control everything. Don't print out about 100 books, keep it small 10 or 20 to start. Present at local bookstore around your neighborhood, library, schools, and etc...
This will help you establish readers, and also let you know how marketable your book really is.
After that, you can re-edit your book base on the feed back and reviews you get. Then maybe you can go to a publisher. A lot of attention doesn't go into first books. Haven't you notice how most authors end up reprinting their old books, once they have publish about 10 books. You think it's a new book only to find out that when you look at the edition, copyright, or printing history, it shows copyright 1998....
Self-publishing is not easy, what you put in is what you get out. A lot of writers started this way, then from word of the mouth and success, ended up with a big publisher.
If you have more questions or looking to promote your book, visit http://www.heavenskyy.com for more information.