Critique Partners: Critique partners are a close group of writers who share their works in progress with each other. The purpose of them reading your manuscript is to give you an in-depth critique. Line editing usually falls to this group. (Although YOU, as the writer, should have line edited that manuscript within an inch of its life before submitting your work to your critique partner for critique). Critique partners are SUPPOSED to find things wrong with your manuscript. Things that need to be fixed, things that don't work, plot holes, voice, characterization, etc. Any issues with your manuscript that an agent or editor would consider a deal breaker. They are not there to catch your typos or grammar issues. YOU should catch those. Read your manuscript out loud (BEFORE sending to your crit partner).
If you've got a critique partner and their only comments are "I love it, it's AWESOME!" for your work, that doesn't really help you grow as a writer. While comments like this, of course, feel wonderful (especially when they mean it), it doesn't do anything to help you polish your manuscript. You might want to consider adding another critique partner.
But, having multiple critique partners brings up a whole new set of problems. What if each partner has different comments? What if the comments contradict what the other one says? This is the point where you, as a writer, must take all of the comments, consider them, ponder them, and decide which is right for your manuscript. If more than one person points out the same issue, then chances are there is an issue that needs to be addressed.
Beta Readers: These are your last line of review before calling the project "done". The main difference between these and critique partners is that these are READERS. The key word: READERS.
These readers read your manuscript after you've polished it until your eyes bleed, after your critique partners have ripped your manuscript to shreds and your polished, revised manuscript has risen from the ashes. These readers give you their overall opinions.
While they might catch a typo/missed word/etc now and then, their purpose is to give global comments with regards to character, plot, voice, etc. The global stuff. Anything that worked, or didn't work. Questions that they asked along the way. Things that they questioned. They are your "big picture" readers. They go into the project not as a writer, but as a reader. Think of them as your first real readers. Don't rely on them to critique your work. In order for them to have it in their hands, you should have already critiqued that bad boy within an inch of it's life.
As with critique partners, it helps to have multiple beta readers so that you can compare and contrast the comments. Again, if multiple readers bring up the same issue, then you potentially have a problem. But ultimately, it is your book and you must do what you feel is right for the story.
I have both critique partners and beta readers for my work. Some writers produce such polished work that they skip the critique partners and go straight to the beta readers. Some have critique partners but don't have beta readers. Personally, I feel that each type of reader has their strengths and bring that to the table when they are reading my manuscript.
On that note - thank you so much to all of my critique partners and beta readers. I love you dearly (even when you make me cry) and would not be at this point in my career without your valuable (yet sometimes painful) feedback.
Writers - What about you? Do you have one, or both types of readers? What do you do about conflicting comments?