I tried bulking agents with fiber first. When those didn't work, I had to take a laxative. But in general, I don't like relying on laxatives because I feel like my bowels will become dependent on them to work. Most laxatives also work too well for me and I end up with diarrhea.
The best solution to pregnancy constipation is more fiber through food. My bowel movements were fairly regular during my second pregnancy because I would eat prunes and dried apricots first thing in the morning followed by a large glass of water. I also made sure that I had at least a salad and several fruits during the day.