I have been trying check the best way, shall I take a direct bus/boat or break the journey at Surat Thani ?
Which of these 2 websites is more reliable ?
http://www.kohsamui-info.com/transportation/coach.html
It shows only one trip from Krabi to Samui and 11 hrs ? The other way much faster but fare is cheaper.
http://www.sawadee.com/transfer/bus-krabi.htm
This one show more trips but fare higher.
Problem is websites seldom let you know when was their last update.
You won't need to break the journey, it's not that far. Krabi town is only about 4 hours drive from the Don Sak pier near Surat Thani, where boats to Samui depart from.
I usually find that the best and easiest way to do it is just go into a travel agent in Krabi a day or two before you wish to depart, and book a combined ticket with them. You could even shop around a few agencies to find the best fare. The price of 290 baht quoted on kohsamui-info.com does sound very reasonable.
For most of us, Surat Thani's just a place in the middle of a longer trip. A place you pass through on the way to or from the Islands.
The longest I have ever spent in Surat Thani is about 6 hours (while waiting for the night boat to Tao or Pha Ngan). I have never noticed anything especially exciting there that might warrant a longer stay. It just looks like an ordinary town. There are other travellers about, but 99.9% of them will be just passing through as #3 points out.