This depends on a variety of factors and I can not recommend a specific one. Euparal is a good general purpose mounting medium, especially suitable for mounting insect parts. The specimens can be directly transferred from concentrated alcohol (in which they were kept) to Euparal on the slide. Other resin based mounting media are not as compatible with alcohol and therefore require additional treatment with xylene, which is not healthy when inhaled. Euparal is yellowish in color, smells quite nice due to the natural oils included, but has a drying time of several weeks, depending on thickness of the mount.