Beta Readers can be a good choice especially if you are a new author. In exchange for an acknowledgement in your book, they will read through it and give you feedback for free.
I have never used a beta reader, but I am editing something for someone right now who is meticulous about them. He is a relatively successful self-published author.
However, a beta reader should not be used in place of a professional editor. (Unless it is a beta reader or nothing because this is your first book and you do not have funds to pay someone.)
Why? Because anyone can be a beta reader and chances are good you will not find a person who gets paid to edit doing it. "Professional" means that not only has the person been paid to do it but that the person is good enough at the job to make living off of it.
Prior to becoming a freelancer, I was a proofreader for the Gutenburg project. I loved doing this, but I think I have done one project this entire past year. I get paid to do proofread, so just as a professional chef may cook a charity meal here and there, s/he is probably not making a gourmet dinner at home every night. (One family I knew where both the mother and father were five star chefs found themselves eating at McDs - a lot. Kind of like editors who write blogs for fun and neglect to edit them... but I am sure you get the picture.)
In addition, you, the author, are going to get paid. You are not a charity. Therefore, what you are getting when you find a beta reader is someone who wants a little bit of fame in exchange for reading your book and giving you their opinion of it. Most professional editors really do not care about fame - they get business more through word of mouth.
Like any skill, editing is something you must train. The more you edit, the fewer mistakes get past you. In addition, if I am getting paid to work on your book, I will force myself to read the entire thing - no matter how awful it is. Then, I will either (1) fix grammar, spelling, and punctuation while leaving comments about things that don't work or (2) fix everything to the best of my ability and leave comments.
If you send it to three or four beta readers before finding a professional, you will save yourself time and money. You will also have a good idea of what more than one person has found wrong with the story. This will be helpful so that when your editor tells you to remove a sex scene you do not balk and say that you wanted it for the shock factor. You will, in fact, already know that everyone who has read it was not shocked but repulsed.