Seaguar Smackdown is the best braid I have ever used. There, I said it. Now before you think I'm just saying that without trying the rest, I have to say I have used just about every major brand out there and there are some really good ones, but Smackdown is awesome.
My two favorite things about it is that is smooth and very thin. I drop shot alot and always use braid with a fluoro leader (8lb Tatsu). As thin as it is, I have moved up to 20lb braid instead of 15lb like I was using and it works great on spinning tackle.
The casting distance, sensitivity and most important durability is due to the fact that this is an eight strand braid. The eight different strands are formed in a perfect circle shape and weaved tightly for maximized abrasion resistance. I'm a big fan of this braid in both green and the bright yellow color. It works great and I have had zero issues after using it for over a year.
The diameter is without question different, look at the chart of the two braids below to see why I am able to use 20lb instead of 15lb.
Other leading braid