There are over 100 cannabinoids in the cannabis plant. Each strain has different proportions of the cannabinoids. I have not tried a lot of strains, but so far White Widow and Sour Diesel seem to be the best ones for bipolar depression.
Sour Diesel takes a little bit longer to act, but both of these strains will give you relief from depression within 25 minutes (vaping). You will feel increased energy and motivation to accomplish things, with minimal side effects.
Note: this is just my experience.
March 12 update: Skywalker OG is far and away the most beneficial stain, for me. I recommend that you try a lot of strains at first.
March 13 update: It feels like one chamber of Skywalker OG gives me a part of my brain back, some part that was missing. It does this within 15 minutes of medicating start time, and it lasts for hours.
More information HERE.