I do different kinds of "workshops", for different reasons.
I have a local critique group. We meet once a month and critique each other's work for that month. Work is emailed before the meeting (about a week before). It's mix of peer/ladder, in terms of abilities.
I like this group because the expectation of having something every month makes sure I have something every month, no matter what else is going on in my over-committed life. We all have similar (spec-fic) genre sensibilities and I get good first cut feedback on the story and the characters.
I do the online Critters and SFF groups. I like Critters because I can get a giant pile of feedback (8 to 16 crits) in a short time (one week plus time in the queue). The feedback is usually at a fairly high level, and I can really look for trends and themes in the feedback. Also, the process of critiquing other people's works has really helped me sharpen my ability to identify and understand what works for me and doesn't work for me in a story.
I only recently joined SFF. For me, the jury is still out. I didn't see a higher level of feedback compared to Critters, and I got less feedback (4 crits in two months) on the story. I get the sense SFF is comprised of smaller groups that critique each other's work and once you're in a group, you're in great shape. We'll see how it goes.
I do Writers Workshops at conventions. This year, I've done Potlatch and Norwescon. I like these because I get feedback from pros who are better than me (like Jay at Potlatch). The feedback is tremendously valuable. I got a lot out of both cons I've been to this year and I think my writing is climbing up a notch because of it.
I'm going to apply for Viable Paradise and Orson Scott Card Bootcamp. They both look good and the thought of spending an entire week doing nothing but writing and talking about writing sounds too good to be true. We'll see if I make it.
So, each form of workshop has its values to me and I've learned a lot from each of them. Your mileage may vary. I'd recommend each of them, in one way or another.