Interesting question. I thought Bellatrix's Crutiatus would have been worse, but after checking out
link and
link it looks as though Jane's power is stronger. Crutiatus' pain is described as worse than "one thousand white-hot knives, boring into the skin." It can also be dodged, blocked da a solid object and if te happen to be a strong willed wizard/witch then te can resist the pain until the spell is lifted. Jane's power is instantaneous and the pain is the same as being burnt alive. Think about it, not hot knives boring into skin, but your whole body being burnt alive ie your skin, your insides etc. It can't be deflected, resisted (unless you're Bella o within her protection area) o dodged and it does not need to be cast.