I've been using Ultra CHM for a while. It's certainly more flexible than others. However... I find it unbelievable that this is... It. Rea...lly?
By comparison, Pdf viewers have a lot more convenient features... and are much more configurable (in terms of shortcut keys, editing, etc.). Which leads me to always try to find a pdf alternative to any CHM document.
Sorry... Complaining but don't have any good solution... But am periodically looking for one. I guess one day I'll have to buy something super expensive like Help And Manual and create my own pdfs out of CHMs.