I found that both Organic and General Chemistry labs helped me. When dealing with solution chemistry, it's easier for me to remember what we did in lab with various solutions and why than memorizing solubility rules. For Organic, if you scan the practice tests, you'll see a handful of questions on lab techniques. If you learn them from a review book, you should be okay, but to me, nothing's better than doing it yourself. When you know what you're doing, you also learn the why and that can only help you understand the procedure you're given on the MCAT.
As for biology, I didn't find the lab all that useful for the MCAT. I had a difficult Bio I teacher so you had to know the material like the back of your hand for lecture so maybe that's why I got more out of lecture than lab. You will have to know some basic lab techniques and it helps if you've done things like electrophoresis, but it's not as prevalent as the Organic lab questions.