Hi Slid .............. unless they've changed it all again recently, they're usually Class 1, 2, and 3.
Class 1 is what hire companies and building firms use. Class 3 are often so flimsy as to be uncomfortable to use.
Go for Class 2. "D" rung (cross-section of rung in the shape of letter D) are usually fine for anyone.
Also, rather than go for one just long enough on full stretch, get one a bit longer. They "feel" a lot better when you're up there.