the Marstrom comes in 6 or 8 mm, in 8 (as shown) or 16 plait (which is smoother). I haven't tried sailing with the 8mm, but I use the 6mm 16 plt version and it seems pretty good to me. The 8mm 8plt is apparently very good, easy to hold and very pliable. It's also a lot cheaper!
I've always used 5 and 7mm Rooster. I've always felt that anything thicker than 7mm and you run the risk of it being too heavy when it gets soaked, and weighs the boom down, especially downwind. Now some might do as I do, and have a light wind and heavy wind mainsheet, but some just can't afford that.
I payed less that $30 for 44ft of 8mm line. I have a job that won't let me visit gym more than twice a week. But it gives me the $30. Or I can quit the job and hit the gym every day. Then I do not need another sheet Choices choices...