The "Sliding CAPTCHA" is simple but tedious to slide the slider to the exact right number.
The "Image rotation CAPTCHA" can be very difficult for some images. (for example I got a wind turbine where the shaft wasn't perfectly vertical in the image, so I had to guess if it should be slightly left or right leaning. I did get it right but I had low confidence)
The "Alphanumeric CAPTCHA" was ok but some of the numbers were fairly obscured. For the one I got (the line ran right though the string, this seems rare, usually it only interacts a few characters).
But not only are these awful for humans it seems like they would be pretty easy to solve for robots. The image one maybe a bit hard, but that was also the least confident for myself.