There is no particular Invisalign tray that will hurt the most or cause more discomfort than others.  Your orthodontist will create each clear aligner to be customized to your mouth and the final goal for your smile.  Typically, most of our patients experience mild discomfort or pain from the pressure being applied by their Invisalign moving their teeth into the correct position.
In most cases, Invisalign trays cause less discomfort than other teeth straightening options.  Keeping your Invisalign in as much as possible will help your teeth get used to the pressure being applied.