I think it depends on the size of the dog you are spaying. I think for big dogs then laparoscopic (key hole) is the way to go, its quicker and less traumatic than open surgery.
For small dogs (say less that 10kg depending on the vet) the benefits of laparoscopic are less - the time saving will be negligible (may actually take longer due to the faff and fiddle of small dogs) and if it is tricky to do this may result in excess rummaging, and consequently more trauma, than just doing a normal abdominal approach.
Dogs usually recover very quickly from open surgery, usually back to their normal selves in 24-48 hours. This is usually quicker with laparoscopic surgery. The other big benefit of laparoscopic surgery is that there is a smaller hole to heal, which doesn't mean they will heal any quicker (wounds heal from side to side not end to end) but means that if the worst happens and she pops her stitches open, there's a lot less space for important stuff to fall out.
Me? If my dog was over 20kg I'd lap spay her, under 10kg I'd do it open, and 10-20kg it would depend on the dog (and for you, what your vet recommends).