Thank you. So which toners are best at boosting contrast in prints, please?
Use of a bleach and redevelop toner - such as sepia toner - can give you a result which appears to increase the range of tones - because the bleaching part tends to lighten the highlights slightly. It is for that reason that the instructions for that type of toner recommend that prints be slightly darker than normal, before toning is done.
However, at least some of the affect is subjective and a matter of perception - warm tones in a print seem to differentiate themselves differently in prints.
I like using brown toner. It doesn't tend to lighten the prints, but the change of tone changes how they appear.