Here's (some) of what I've done:
Online Critique Group: An evolving group of 4-7 writers of different genres and experience levels. Every week, or whenever we have something to post, we submit a chapter or two (4-6k words), and each member posts their critique within a week (mostly).
Pros: Weekly feedback to spur you on; long-term relationships mean you're familiar with the author and their work; three or four perspectives on every chapter.
Cons: Only small chunks of an MS can be critiqued at a time. Not everyone can critique or submit every week. Writers out-of-genre might have a hard time critiquing each other.
Critique Partners: A one-on-one swap of anything from first chapters to partials to full MS. Often I'll critique someone's full MS, and they will critique mine months later (or vice versa), whenever each of us is ready (and in need of a critique).
Pros: Thorough feedback of a complete MS; the commitment to critique often builds long-term relationships.
Cons: Only one perspective; sometimes you don't know if the author is a good match before critiquing.
Face-to-Face Critique Group: On the third Wednesday each month, my local SCBWI group meets face to face. Anywhere from 9-13 people show up, each with a dozen copies of 5 pages of their WiP (beginning, middle, or end). We read our pages aloud, or split the pages among five others, who read aloud for us. Everyone makes notes on their copies, and there's about 5 minutes for verbal feedback after the reading.
Pros: Instant feedback from a dozen different people; verbal feedback during a read (Oohs! Aahs! Ha!) can help you judge the timing of your work; works well for openings (the first 5 pages), less so for subsequent pages, where more background is necessary.In truth, I highly value all these different forms of crits, each in their own way helping me grow as an author, and enabling me to help other authors grow as well.
Cons: Only critique very short pieces of work; sometimes a group will reverberate off itself, with independent (conflicting) perspectives not as easily drawn out; only meet once a month.
What crit forms have you used? And what do you see as the pros and cons?