I havethe cheaper Tri-Sharp
http://3.bp.blogspot.com/_3hpkFU3hD0...1600/blade.jpg
But the truth is I only use it when I remember I have it and can dig it out of the quilt-related junk drawer
I buy the Olfa rotary blades in quantity on eBay, so my cost per blade is really low (usually ~$1).
I know how to cut well, almost never nick the blade, and so if it gets dull, I just toss it and put in a new one.