I think everyone is different! I have not used movicol, but as I have IBS tried fybogel and couldn't leave the loo for 2 days!! I use lactulose (small amount) every day, it softens and regulates so I only go once a day which is better than 10 times (when using fybogel!!!). I think it's just a matter of trying stuff out :D

I guess like everyone else said, it is a matter of what suits your body more. When i first went to my doctor (Hernia, AF and Hemorrhoids) the first thing he told me was that we need to deal with the constipation first. Mind you it was a 5 months long constipation that varied in terms of severity.
If anything, Lactulose made my problem worse! It would work for a day or two, then stop, i would increase the dose (I was already on a 3 x 15 ml dose a day ) **WARNING: This Part Gets Graphic** and that would give me diarrhea, not soft stools, no pellet shaped, runny and very awful to just pass. They were just hard it didn't work as a softener at all. But perhaps that's my body's reaction because i have been on Movicol for 5 days and i just wish i knew it before. My AF got worse last week if i knew Movicol by then i would have probably avoided the pain because i am already doing ok in terms of stool, but i am afraid my AF needs surgery now.
So go ahead and try lactulose, Movicol is not meant to be a long term laxative as far as i know (perhaps others can correct me if i am wrong?) but Lactulose however is safe to use for prolonged times. For me it was very mild and almost ineffective.