I like to give Juhani Master Critical Strike, and equip 2 lightsabers to her, each one with a Nextor and an Opila (as the game allows you to obtain 2 of each). If you equip a Nextor and an Opila crystal on the same lightsaber, and the party member with that lightsaber equipped also has the Critical Strike feat (ideally Master Critical Strike), you get a compound effect from the various properties which is extremely powerful - basically a huge chance of inflicting a Critical attack which will also be a particularly high-powered Critical attack.