Someone recently asked me how useful peer critique groups are, as opposed to professional critiques (such as the ones people pay for at SCBWI conferences). Did I see one as more valuable than the other, especially if the peers in question have not published yet?
There's no simple answer to this question, since many factors come into play. But my shortest answer would be: It's not necessary to limit oneself to professional critiques.
A professional editor is likely to give an excellent critique, because it's one of the things editors do for a living. And yet, I've still heard of people being disappointed after paying for a professional editor critique. Sometimes it's because the editor didn't click with the manuscript--and it's harder to give constructive criticism for the kind of story you don't read a lot. (This sometimes happen at conferences, when an editor who doesn't handle historical manuscripts might receive a historical novel, or when an editor who favors gritty YA gets a sweet chapter book.) Sometimes the editor's style just doesn't mesh well with the writer's. The writer may want a certain style or category of feedback, and the editor approaches critique from a different angle altogether.
Editors aren't the only source of professional feedback. Some agents help their clients edit manuscripts, while other agents are very hands-off. Similarly, some writers like agent feedback and others prefer their agents to stick to contract-related matters. It's all a question of what works best for the pair involved.
Our fellow writers, whether published or not, have a wide variety of critiquing skills. The best writer in a room isn't necessarily the best critiquer, and isn't necessarily the best fit for every manuscript.
Some writers know they want a brutal dissection of their work; they don't take anything personally and need no pats on the back. They are best off finding critiquers who will dish out such critiques, no holds barred. But for most of us, a mix of different styles can be helpful. Different people pick up on different things. Some focus on plot problems while others notice problems with setting, and still others have an ear for dialogue. Some critiquers are quick to praise and others are hard to please; in such cases, a writer knows that if the "easy" critiquer finds something problematic, it really is a problem. And praise from the tough critic is a sign that the manuscript is ready.
The best thing to look for in a critiquer is a careful reader who can give feedback in a style most suited to the writer. Familiarity with the current literature and the industry are pluses, but that doesn't mean the critiquer has to be an editor, agent, or published writer.