My experience is that it almost doesn't matter what strain I choose, it aids in falling asleep or getting back to sleep. It happened to me last night. I'm still relatively new, finding what works for me and what doesn't.
My truth is that I need to employ other means as well, for successful slumber. Moderate exercise, at least three times a week, is fantastic. I also practice deep breathing and meditation.
I know the effects of what I have and still chose a straight Sativa last night (Golden Tiger X Panama). The effects are what you'd expect, as compared to an Indica. It didin't matter. I enjoyed my complex, thought provoking, slightly invigorating high and gradually drifted off...
I guess my point is, don't get too wrapped around the axle about the strain. If you do the other things (meditation, etc.), you'll get to sleep regardless of strain.