"I have to carry it on my daypack when I am trekking. Which one do you recommend 4 sections or 3 sections?"
Another point that you may want to consider in 3 vs 4 sections is speed of setup. For those who are able to plan every shot, this may be less important, but for me in nature, wildlife, or landscape photography, I often encounter opportunities where a tripod is needed and I only have seconds to get it set up (e.g. quickly changing light). It is a lot faster to loosen and tighten 9 joints than it is 12.
I usually prefer legs with the "snap-locks" (I forget the term) over twist-locks because of speed. However, I have found that I can set up a 3-section Gitzo GT1930 NEARLY as fast as I can my old Velbon 4-section with snap-locks. The additional length of the Gitzo has not bothered me when carrying it on a backpack. I don't often go through heavy brush with it either, which could cause trouble if it stuck up too far and snagged on trees or brush.