I've recently done a rather large-scale revision and now it's out with quite a number of guinea pigs--er, critiquers--who I hope don't regret volunteering for the job. Now I'm waiting rather nervously and trying not to think about the reactions I'm going to get. I like getting critiques because I want to improve, but I have a hope that someday I'll pass inspection, at least with an A-. Anyhow, I've been thinking of the kinds of critiquers one could choose, and their usefulness (or not). So here's my evaluation. (And in case you're wondering, I sent my ms to all awesome critiquers!)
The reader who loves you and can't bear to criticize anything. They don't get how critiques work. They can be great ego-boosters if they like it, but if they don't, you are unlikely to ever hear the title of your work ever cross their lips. I had one like that once. If I were to attempt another crit with this person, I'd make a list of question for them to answer so they didn't feel afraid of a personal attack.
The reader who thinks a critique is ONLY a criticism. Again, not so helpful, because if you don't know what you're doing right, you don't know what direction to go in. A good critique lets you know the good stuff, too. I haven't had one of these, but I've known people who have.
The reader who doesn't get the book/genre. This can be a very frustrating experience. The reader wants something that you were never intending to write, and their comments are either critical because you aren't doing that, or suggesting you change the very nature of your story. Again, questions here would be helpful for the reader. Unfortunately you usually don't realize this until you get your critique back.
On the other hand, the reader who doesn't normally read your genre can be a useful kind of critiquer because they will notice things that other minds will skim over out of familiarity with the conventions. They can be very helpful in recognizing how well the story works as a story. So don't discount this critiquer!
The reader whose writing ability/publishing experience is slightly above yours. Awesome. Remember to be this critiquer for someone else as well.
The reader who is an expert on some technical element of your story. Again, awesome. Although, realize that while they might be a trained psychologist, they may not be a trained plot-ologist. But if you have an expert on hand for some element of your story, that's a good thing.
The reader who reads widely in your genre and connects with the main point of what you're trying to do with your book, and who also can articulate themselves well. Awesome. Bingo, bingo, bingo.