The author needs to think about what it is they want. For example, what are your goals?
Get the book into print?
Want it to be available to the world, major book stores and buyers?     
Do you want editing services?
Do you need a book cover designed?
Do you want help in setting up book signings?
Want an audio version?
How about an e-book?
Help in marketing your book before and after the release? 
Facts:
There’re a lot of methods / ways to get your book in print. There use to be just three ways. 
Vanity, Subsidy and Traditional.  But ALL the publishers are changing
their business model and their services often fall into other categories. 
You can no longer apply set standards to the three types. They need to keep up with the latest trends. 
So look at each publishing company and the list of services that they will offer. That list could be,

    Editing. This is so very important. Nothing says stupid like a bad manuscript.
    
    Book cover design. If you book cover look bad, so will your sale numbers.
    
    Marketing services. A new author might have some trouble figuring this part out on their own, 
    because not everybody is a marketing expert. Help is needed.
    
    Audio books. This is the hottest and newest market coming from the publishing world.
    
    E-books. The neatest way for buyer on the move to get a book to read while they travel.
    
    Distributors. This is a relationship for publishers and buyers only. 
    Rarely does an author work with a distributor one on one. 
    An author needs a publisher that has a strong relationship with a distributor. 

ALL of these services cost money.

If you start at Vanity historically you’ll get a very limited list of services. 
They basically print the book, no editing, no design etc. The price is what ever 
they charge.  Hopefully it reflects what services they’re offering.  
Some Vanity publishers offer more than others.Subsidy, on the other hand offers 
a little more. But you have to look at just what it is that they‘re offering. 

Traditional  publishers are touted as ones who offers advances, the authors never pay anything 
and thru their process it legitimizes one as a “published” author. Traditional publisher are 
changing too. However the facts are that waiting for them to discover you may never happen. 
And as stated in another posting this is not the only way to become a published author.
    
These three types of publishers are fast changing into hybrids. Anything goes.
The prices are changing too. The old adage, you get what you pay for is a fact.
Weight out what you’re getting for the price. The more options you get the better the 
chances are for your book to be a success.