I personally don't do well with any of those bars. To me, they are practically candy bars. They are over very quickly, don't fill me and I feel as if I haven't eaten. Plus they leave me clamoring for MORE of them. Not good. I need lots of filling power and VOLUME from my calories. So for me, the best way to get in lots of fiber is to eat LOTS & LOTS of veggies and some fruits & beans as well. There's also whole grains, which I tend to avoid though, they are perfectly fine for most. I have never, not one day since changing my diet, have suffered from constipation. I would have my good friends - veggies to thank for that.
I would ask you, what does your daily menu look like? How much fruits, veggies, beans and whole grains are you eating?
ALL fruits and veggies have fiber, some more then others. Here's a partial list of some high fiber foods.
http://www.bellaonline.com/articles/art49479.asp
I urge you to incorporate as many as possible into your diet. Oh and don't forget to drink lots of water when you do so. Fiber expands in the stomach and you'll need the extra water. On top of all the "bathroom benefits", fiber is essential to good health and is a weight loss powerhouse.