While I have found a strain (Skywalker OG) that best meets my needs regarding depression, motivation and energy, I have also found that it’s ideal to keep changing strains every 5 to 15g, because each strain supplies motivation to a different category of productivity in the brain.
If you suffer from bipolar depression, a variety of strains might provide a spectrum of motivation-related benefits across time for you. You will be motivated variously through philosophical thinking, long-term planning, organizing your routine, doing major tasks, and doing minor chores.
Always remember to schedule downtime (rest or recreation), because marijuana can give you so much motivation and energy that you forget to rest, and you are at risk of burning out.
(Original thoughts here.)