what is the difference between these two pipes. they look very simaler.

 

One is made by CT Racing, one is made by Alba....
Seriously though, they're both steel (Graydon muffler is alum), ceramic coated, and use disks, so the power difference between the two should be minimal.
My advise is to use 18 disks, no matter which pipe you choose. I ran 18 disks on my RWR pipe, played with all combinations of disks and jetting, got the best performance throughout entire rev range with 18 disks.
I'll not own another ceramic coated pipe again though - too many problems down the road with the coating coming off, with all brands from what I've heard and read. Only stainless steel for me from now on. Worst areas for rusting on ceramic pipes is where the pipes connect together - the ceramic is gone from here in no time, and then they rust from the inside out. I run a Yoshimura now, all stainless.