Personaly I like silver and viridian. Blue is good to have in a saber. If I had to pick a favorite color for my most used saber of all the kotor colors it would be silver. For my 2nd saber or droid saber on the game viridian. In real life I would use a silver and a viridian in my double blades. For those of you that are wondering I still dual wield double blades. Progress is progressing slow on my skills with them but none the less progressing. I'm gonna start a topic on it soon to post katas and different attacks and suggestions on how to master dual wielding double blades. Back to the crystals. This is the equation I use.

Blue:fighter
Green:force user/adept
Yellow:force and fighter blanced out
Red:Sith or powerful saber
Orange:highly skilled fighter
silver:most used saber
viridian:droid saber
white:no agenda
cyan:fights very little or has little agenda
bronze:saber user seen a great deal of combat

For those of you who aren't sure how to get the bronze crystal, I got mine from mandalore when he gives you a lightsaber. Best way to get the saber you want is to save before you get one from any one. If you don't get it reload the game. Also to get a double blade 99% of the time lose the fight with revan in the tomb, you won't die but you will be weak and should get a double blade. Any way thats my theory on the crystal colors. If I don't use that theory I use personal preference or what I think looks best on the each character.