I do have an assortment of clay blades but more often than not use my own trusty blade. It's a snap off knife blade which I have made a polymer clay handle for. I have used several of these over the years (have only just stopped using the first one I made 20 years ago!) and find them very useful. The are sharp, rigid, cheap and easy to get hold of. The point makes it more versatile than a standard clay blade. I now make the handle with a flat bottom so they stand up on the table. I use the wider blades ( about 18mm across) as they are more rigid.
Although the blade is meant to snap off it won't unless you try to bend or curve the blade. For cutting and downward pressure there is no risk of snapping. As I say I've been using one for 20 years and never had any problem.
What do you use to cut your clay?